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 $218.83   13.738%   $248.8929   $248.89   $248.90   $248.90  
  Purchase #2 $110.78   6.511%   $117.9929   $117.99   $118.00   $118.00  
  Purchase #3 $210.31   4.828%   $220.4638   $220.46   $220.45   $220.50  
  Purchase #4 $165.25   13.750%   $187.9719   $187.97   $187.95   $188.00  
  Purchase #5 $61.42   10.166%   $67.664   $67.66   $67.65   $67.70  
  Purchase #6 $228.49   8.782%   $248.556   $248.56   $248.55   $248.60  
  Purchase #7 $163.97   8.289%   $177.5615   $177.56   $177.55   $177.60  
  7 purchase totals = $1,159.05       $1,269.1030   $1,269.09   $1,269.05   $1,269.30