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 $194.26   11.201%   $216.0191   $216.02   $216.00   $216.00  
  Purchase #2 $136.54   13.251%   $154.6329   $154.63   $154.65   $154.60  
  Purchase #3 $248.77   3.838%   $258.3178   $258.32   $258.30   $258.30  
  Purchase #4 $179.69   6.130%   $190.705   $190.71   $190.70   $190.70  
  Purchase #5 $135.30   6.523%   $144.1256   $144.13   $144.15   $144.10  
  Purchase #6 $12.49   6.775%   $13.3362   $13.34   $13.35   $13.30  
  Purchase #7 $14.57   7.506%   $15.6636   $15.66   $15.65   $15.70  
  7 purchase totals = $921.62       $992.8002   $992.81   $992.80   $992.70