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 $85.63   11.322%   $95.325   $95.33   $95.35   $95.30  
  Purchase #2 $22.70   10.276%   $25.0327   $25.03   $25.05   $25.00  
  Purchase #3 $55.72   3.519%   $57.6808   $57.68   $57.70   $57.70  
  Purchase #4 $129.54   9.306%   $141.595   $141.60   $141.60   $141.60  
  Purchase #5 $185.66   7.681%   $199.9205   $199.92   $199.90   $199.90  
  Purchase #6 $209.62   11.295%   $233.2966   $233.30   $233.30   $233.30  
  Purchase #7 $92.50   6.829%   $98.8168   $98.82   $98.80   $98.80  
  7 purchase totals = $781.37       $851.6674   $851.68   $851.70   $851.60