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 $53.48   10.236%   $58.9542   $58.95   $58.95   $59.00  
  Purchase #2 $43.92   13.744%   $49.9564   $49.96   $49.95   $50.00  
  Purchase #3 $200.82   9.594%   $220.0867   $220.09   $220.10   $220.10  
  Purchase #4 $75.50   7.453%   $81.127   $81.13   $81.15   $81.10  
  Purchase #5 $7.77   7.105%   $8.3221   $8.32   $8.30   $8.30  
  Purchase #6 $36.62   7.169%   $39.2453   $39.25   $39.25   $39.20  
  Purchase #7 $214.62   10.577%   $237.3204   $237.32   $237.30   $237.30  
  7 purchase totals = $632.73       $695.0121   $695.02   $695.00   $695.00