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 $57.58   10.827%   $63.8142   $63.81   $63.80   $63.80  
  Purchase #2 $180.86   6.732%   $193.0355   $193.04   $193.05   $193.00  
  Purchase #3 $180.86   9.216%   $197.5281   $197.53   $197.55   $197.50  
  Purchase #4 $12.56   11.782%   $14.0398   $14.04   $14.05   $14.00  
  Purchase #5 $47.68   6.690%   $50.8698   $50.87   $50.85   $50.90  
  Purchase #6 $189.98   9.491%   $208.011   $208.01   $208.00   $208.00  
  Purchase #7 $191.60   7.817%   $206.5774   $206.58   $206.60   $206.60  
  7 purchase totals = $861.12       $933.8758   $933.88   $933.90   $933.80