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 $71.54   4.799%   $74.9732   $74.97   $74.95   $75.00  
  Purchase #2 $180.86   13.128%   $204.6033   $204.60   $204.60   $204.60  
  Purchase #3 $76.47   12.381%   $85.9378   $85.94   $85.95   $85.90  
  Purchase #4 $219.42   10.325%   $242.0751   $242.08   $242.10   $242.10  
  Purchase #5 $150.89   9.413%   $165.0933   $165.09   $165.10   $165.10  
  Purchase #6 $74.42   7.801%   $80.2255   $80.23   $80.25   $80.20  
  Purchase #7 $57.63   11.525%   $64.2719   $64.27   $64.25   $64.30  
  7 purchase totals = $831.23       $917.1801   $917.18   $917.20   $917.20