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 $241.97   10.402%   $267.1397   $267.14   $267.15   $267.10  
  Purchase #2 $194.88   13.740%   $221.6565   $221.66   $221.65   $221.70  
  Purchase #3 $110.86   9.152%   $121.0059   $121.01   $121.00   $121.00  
  Purchase #4 $44.56   6.268%   $47.353   $47.35   $47.35   $47.40  
  Purchase #5 $33.92   5.825%   $35.8958   $35.90   $35.90   $35.90  
  Purchase #6 $117.27   7.184%   $125.6947   $125.69   $125.70   $125.70  
  Purchase #7 $65.85   5.131%   $69.2288   $69.23   $69.25   $69.20  
  7 purchase totals = $809.31       $887.9744   $887.98   $888.00   $888.00