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 $197.96   6.668%   $211.16   $211.16   $211.15   $211.20  
  Purchase #2 $159.41   11.418%   $177.6114   $177.61   $177.60   $177.60  
  Purchase #3 $167.91   13.461%   $190.5124   $190.51   $190.50   $190.50  
  Purchase #4 $207.69   8.653%   $225.6614   $225.66   $225.65   $225.70  
  Purchase #5 $104.40   11.451%   $116.3548   $116.35   $116.35   $116.40  
  Purchase #6 $230.65   11.554%   $257.2993   $257.30   $257.30   $257.30  
  Purchase #7 $132.98   11.435%   $148.1863   $148.19   $148.20   $148.20  
  7 purchase totals = $1,201.00       $1,326.7856   $1,326.78   $1,326.75   $1,326.90