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 $57.76   7.803%   $62.267   $62.27   $62.25   $62.30  
  Purchase #2 $58.57   12.185%   $65.7068   $65.71   $65.70   $65.70  
  Purchase #3 $171.50   13.453%   $194.5719   $194.57   $194.55   $194.60  
  Purchase #4 $46.35   6.224%   $49.2348   $49.23   $49.25   $49.20  
  Purchase #5 $185.88   10.306%   $205.0368   $205.04   $205.05   $205.00  
  Purchase #6 $27.25   5.634%   $28.7853   $28.79   $28.80   $28.80  
  Purchase #7 $101.93   9.764%   $111.8824   $111.88   $111.90   $111.90  
  7 purchase totals = $649.24       $717.4850   $717.49   $717.50   $717.50