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 $138.91   5.642%   $146.7473   $146.75   $146.75   $146.70  
  Purchase #2 $213.25   13.452%   $241.9364   $241.94   $241.95   $241.90  
  Purchase #3 $48.50   4.300%   $50.5855   $50.59   $50.60   $50.60  
  Purchase #4 $118.70   5.814%   $125.6012   $125.60   $125.60   $125.60  
  Purchase #5 $30.65   13.319%   $34.7323   $34.73   $34.75   $34.70  
  Purchase #6 $169.78   13.545%   $192.7767   $192.78   $192.80   $192.80  
  Purchase #7 $217.38   3.382%   $224.7318   $224.73   $224.75   $224.70  
  7 purchase totals = $937.17       $1,017.1112   $1,017.12   $1,017.20   $1,017.00