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 $44.69   7.172%   $47.8952   $47.90   $47.90   $47.90  
  Purchase #2 $191.64   4.160%   $199.6122   $199.61   $199.60   $199.60  
  Purchase #3 $75.48   3.428%   $78.0675   $78.07   $78.05   $78.10  
  Purchase #4 $229.54   11.563%   $256.0817   $256.08   $256.10   $256.10  
  Purchase #5 $192.63   5.528%   $203.2786   $203.28   $203.30   $203.30  
  Purchase #6 $113.44   9.645%   $124.3813   $124.38   $124.40   $124.40  
  Purchase #7 $130.92   11.226%   $145.6171   $145.62   $145.60   $145.60  
  7 purchase totals = $978.34       $1,054.9336   $1,054.94   $1,054.95   $1,055.00