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 $224.42   10.663%   $248.3499   $248.35   $248.35   $248.30  
  Purchase #2 $184.74   12.715%   $208.2297   $208.23   $208.25   $208.20  
  Purchase #3 $152.42   7.590%   $163.9887   $163.99   $164.00   $164.00  
  Purchase #4 $127.72   12.345%   $143.487   $143.49   $143.50   $143.50  
  Purchase #5 $69.71   8.413%   $75.5747   $75.57   $75.55   $75.60  
  Purchase #6 $86.29   11.219%   $95.9709   $95.97   $95.95   $96.00  
  Purchase #7 $151.80   9.353%   $165.9979   $166.00   $166.00   $166.00  
  7 purchase totals = $997.10       $1,101.5988   $1,101.60   $1,101.60   $1,101.60