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 $60.87   11.596%   $67.9285   $67.93   $67.95   $67.90  
  Purchase #2 $182.70   9.844%   $200.685   $200.69   $200.70   $200.70  
  Purchase #3 $195.59   12.489%   $220.0172   $220.02   $220.00   $220.00  
  Purchase #4 $30.86   6.831%   $32.968   $32.97   $32.95   $33.00  
  Purchase #5 $233.94   8.168%   $253.0482   $253.05   $253.05   $253.00  
  Purchase #6 $141.66   13.836%   $161.2601   $161.26   $161.25   $161.30  
  Purchase #7 $48.89   8.484%   $53.0378   $53.04   $53.05   $53.00  
  7 purchase totals = $894.51       $988.9448   $988.96   $988.95   $988.90