Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $110.71   3.502%   $114.5871   $114.59   $114.60   $114.60  
  Purchase #2 $234.86   4.861%   $246.2765   $246.28   $246.30   $246.30  
  Purchase #3 $187.59   7.671%   $201.98   $201.98   $202.00   $202.00  
  Purchase #4 $152.85   12.154%   $171.4274   $171.43   $171.45   $171.40  
  Purchase #5 $116.48   4.239%   $121.4176   $121.42   $121.40   $121.40  
  Purchase #6 $159.49   11.371%   $177.6256   $177.63   $177.65   $177.60  
  Purchase #7 $209.55   9.571%   $229.606   $229.61   $229.60   $229.60  
  7 purchase totals = $1,171.53       $1,262.9202   $1,262.94   $1,263.00   $1,262.90