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 $173.49   12.739%   $195.5909   $195.59   $195.60   $195.60  
  Purchase #2 $213.93   9.503%   $234.2598   $234.26   $234.25   $234.30  
  Purchase #3 $155.25   9.491%   $169.9848   $169.98   $170.00   $170.00  
  Purchase #4 $167.69   11.602%   $187.1454   $187.15   $187.15   $187.10  
  Purchase #5 $90.49   10.282%   $99.7942   $99.79   $99.80   $99.80  
  Purchase #6 $229.62   13.347%   $260.2674   $260.27   $260.25   $260.30  
  Purchase #7 $163.48   10.566%   $180.7533   $180.75   $180.75   $180.80  
  7 purchase totals = $1,193.95       $1,327.7958   $1,327.79   $1,327.80   $1,327.90