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 $55.40   12.255%   $62.1893   $62.19   $62.20   $62.20  
  Purchase #2 $186.46   3.621%   $193.2117   $193.21   $193.20   $193.20  
  Purchase #3 $230.67   11.222%   $256.5558   $256.56   $256.55   $256.60  
  Purchase #4 $140.96   7.660%   $151.7575   $151.76   $151.75   $151.80  
  Purchase #5 $129.95   8.159%   $140.5526   $140.55   $140.55   $140.60  
  Purchase #6 $89.60   13.145%   $101.3779   $101.38   $101.40   $101.40  
  Purchase #7 $32.81   10.510%   $36.2583   $36.26   $36.25   $36.30  
  7 purchase totals = $865.85       $941.9031   $941.91   $941.90   $942.10