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 $59.73   12.510%   $67.2022   $67.20   $67.20   $67.20  
  Purchase #2 $208.39   6.140%   $221.1851   $221.19   $221.20   $221.20  
  Purchase #3 $169.40   11.187%   $188.3508   $188.35   $188.35   $188.40  
  Purchase #4 $183.46   10.313%   $202.3802   $202.38   $202.40   $202.40  
  Purchase #5 $250.32   6.323%   $266.1477   $266.15   $266.15   $266.10  
  Purchase #6 $8.31   11.117%   $9.2338   $9.23   $9.25   $9.20  
  Purchase #7 $117.94   10.802%   $130.6799   $130.68   $130.70   $130.70  
  7 purchase totals = $997.55       $1,085.1797   $1,085.18   $1,085.25   $1,085.20