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 $212.62   11.286%   $236.6163   $236.62   $236.60   $236.60  
  Purchase #2 $51.49   13.516%   $58.4494   $58.45   $58.45   $58.40  
  Purchase #3 $80.96   13.387%   $91.7981   $91.80   $91.80   $91.80  
  Purchase #4 $56.60   8.283%   $61.2882   $61.29   $61.30   $61.30  
  Purchase #5 $169.87   10.785%   $188.1905   $188.19   $188.20   $188.20  
  Purchase #6 $189.34   12.574%   $213.1476   $213.15   $213.15   $213.10  
  Purchase #7 $159.33   4.656%   $166.7484   $166.75   $166.75   $166.70  
  7 purchase totals = $920.21       $1,016.2385   $1,016.25   $1,016.25   $1,016.10