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 $64.43   6.619%   $68.6946   $68.69   $68.70   $68.70  
  Purchase #2 $197.67   12.203%   $221.7917   $221.79   $221.80   $221.80  
  Purchase #3 $91.69   6.136%   $97.3161   $97.32   $97.30   $97.30  
  Purchase #4 $195.56   3.817%   $203.0245   $203.02   $203.00   $203.00  
  Purchase #5 $42.44   8.376%   $45.9948   $45.99   $46.00   $46.00  
  Purchase #6 $142.42   12.255%   $159.8736   $159.87   $159.85   $159.90  
  Purchase #7 $150.32   6.833%   $160.5914   $160.59   $160.60   $160.60  
  7 purchase totals = $884.53       $957.2867   $957.27   $957.25   $957.30