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 $50.62   9.589%   $55.474   $55.47   $55.45   $55.50  
  Purchase #2 $53.69   8.521%   $58.2649   $58.26   $58.25   $58.30  
  Purchase #3 $168.25   4.566%   $175.9323   $175.93   $175.95   $175.90  
  Purchase #4 $211.79   4.546%   $221.418   $221.42   $221.40   $221.40  
  Purchase #5 $107.86   12.532%   $121.377   $121.38   $121.40   $121.40  
  Purchase #6 $196.62   5.641%   $207.7113   $207.71   $207.70   $207.70  
  Purchase #7 $153.39   11.130%   $170.4623   $170.46   $170.45   $170.50  
  7 purchase totals = $942.22       $1,010.6398   $1,010.63   $1,010.60   $1,010.70