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 $57.93   8.697%   $62.9682   $62.97   $62.95   $63.00  
  Purchase #2 $121.58   8.211%   $131.5629   $131.56   $131.55   $131.60  
  Purchase #3 $16.67   11.541%   $18.5939   $18.59   $18.60   $18.60  
  Purchase #4 $143.30   12.548%   $161.2813   $161.28   $161.30   $161.30  
  Purchase #5 $87.37   7.395%   $93.831   $93.83   $93.85   $93.80  
  Purchase #6 $9.78   9.544%   $10.7134   $10.71   $10.70   $10.70  
  Purchase #7 $8.54   8.245%   $9.2441   $9.24   $9.25   $9.20  
  7 purchase totals = $445.17       $488.1948   $488.18   $488.20   $488.20