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 $55.99   6.497%   $59.6277   $59.63   $59.65   $59.60  
  Purchase #2 $168.57   6.814%   $180.0564   $180.06   $180.05   $180.10  
  Purchase #3 $150.39   11.485%   $167.6623   $167.66   $167.65   $167.70  
  Purchase #4 $77.42   7.203%   $82.9966   $83.00   $83.00   $83.00  
  Purchase #5 $174.77   11.102%   $194.173   $194.17   $194.15   $194.20  
  Purchase #6 $119.93   5.202%   $126.1688   $126.17   $126.15   $126.20  
  Purchase #7 $201.89   9.676%   $221.4249   $221.42   $221.40   $221.40  
  7 purchase totals = $948.96       $1,032.1097   $1,032.11   $1,032.05   $1,032.20