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 $97.45   13.622%   $110.7246   $110.72   $110.70   $110.70  
  Purchase #2 $110.28   11.227%   $122.6611   $122.66   $122.65   $122.70  
  Purchase #3 $77.80   4.772%   $81.5126   $81.51   $81.50   $81.50  
  Purchase #4 $217.76   6.733%   $232.4218   $232.42   $232.40   $232.40  
  Purchase #5 $80.55   6.138%   $85.4942   $85.49   $85.50   $85.50  
  Purchase #6 $168.59   9.330%   $184.3194   $184.32   $184.30   $184.30  
  Purchase #7 $237.47   11.828%   $265.558   $265.56   $265.55   $265.60  
  7 purchase totals = $989.90       $1,082.6917   $1,082.68   $1,082.60   $1,082.70