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 $179.71   12.126%   $201.5016   $201.50   $201.50   $201.50  
  Purchase #2 $97.71   6.805%   $104.3592   $104.36   $104.35   $104.40  
  Purchase #3 $33.62   4.336%   $35.0778   $35.08   $35.10   $35.10  
  Purchase #4 $94.86   10.226%   $104.5604   $104.56   $104.55   $104.60  
  Purchase #5 $54.43   9.297%   $59.4904   $59.49   $59.50   $59.50  
  Purchase #6 $244.94   4.677%   $256.3958   $256.40   $256.40   $256.40  
  Purchase #7 $161.34   5.623%   $170.4121   $170.41   $170.40   $170.40  
  7 purchase totals = $866.61       $931.7973   $931.80   $931.80   $931.90