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 $57.62   7.515%   $61.9501   $61.95   $61.95   $62.00  
  Purchase #2 $121.26   10.361%   $133.8237   $133.82   $133.80   $133.80  
  Purchase #3 $213.39   12.617%   $240.3134   $240.31   $240.30   $240.30  
  Purchase #4 $139.48   4.134%   $145.2461   $145.25   $145.25   $145.20  
  Purchase #5 $28.83   5.784%   $30.4975   $30.50   $30.50   $30.50  
  Purchase #6 $244.69   13.326%   $277.2974   $277.30   $277.30   $277.30  
  Purchase #7 $51.50   4.533%   $53.8345   $53.83   $53.85   $53.80  
  7 purchase totals = $856.77       $942.9627   $942.96   $942.95   $942.90