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 $60.78   8.229%   $65.7816   $65.78   $65.80   $65.80  
  Purchase #2 $40.85   13.279%   $46.2745   $46.27   $46.25   $46.30  
  Purchase #3 $236.54   6.371%   $251.61   $251.61   $251.60   $251.60  
  Purchase #4 $31.87   8.365%   $34.5359   $34.54   $34.55   $34.50  
  Purchase #5 $206.48   3.427%   $213.5561   $213.56   $213.55   $213.60  
  Purchase #6 $93.71   3.865%   $97.3319   $97.33   $97.35   $97.30  
  Purchase #7 $179.28   11.341%   $199.6121   $199.61   $199.60   $199.60  
  7 purchase totals = $849.51       $908.7021   $908.70   $908.70   $908.70