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 $174.31   11.395%   $194.1726   $194.17   $194.15   $194.20  
  Purchase #2 $132.72   12.545%   $149.3697   $149.37   $149.35   $149.40  
  Purchase #3 $60.56   3.115%   $62.4464   $62.45   $62.45   $62.40  
  Purchase #4 $206.86   8.543%   $224.532   $224.53   $224.55   $224.50  
  Purchase #5 $189.32   4.110%   $197.1011   $197.10   $197.10   $197.10  
  Purchase #6 $236.73   10.222%   $260.9285   $260.93   $260.95   $260.90  
  Purchase #7 $199.62   13.161%   $225.892   $225.89   $225.90   $225.90  
  7 purchase totals = $1,200.12       $1,314.4423   $1,314.44   $1,314.45   $1,314.40