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 $95.27   9.487%   $104.3083   $104.31   $104.30   $104.30  
  Purchase #2 $243.55   8.687%   $264.7072   $264.71   $264.70   $264.70  
  Purchase #3 $32.64   8.436%   $35.3935   $35.39   $35.40   $35.40  
  Purchase #4 $119.54   10.431%   $132.0092   $132.01   $132.00   $132.00  
  Purchase #5 $187.38   9.824%   $205.7882   $205.79   $205.80   $205.80  
  Purchase #6 $164.32   9.620%   $180.1276   $180.13   $180.15   $180.10  
  Purchase #7 $35.29   12.679%   $39.7644   $39.76   $39.75   $39.80  
  7 purchase totals = $877.99       $962.0984   $962.10   $962.10   $962.10