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 $66.68   7.132%   $71.4356   $71.44   $71.45   $71.40  
  Purchase #2 $58.38   13.223%   $66.0996   $66.10   $66.10   $66.10  
  Purchase #3 $212.65   13.872%   $242.1488   $242.15   $242.15   $242.10  
  Purchase #4 $125.77   7.230%   $134.8632   $134.86   $134.85   $134.90  
  Purchase #5 $102.48   12.731%   $115.5267   $115.53   $115.55   $115.50  
  Purchase #6 $122.33   11.451%   $136.338   $136.34   $136.35   $136.30  
  Purchase #7 $168.94   12.347%   $189.799   $189.80   $189.80   $189.80  
  7 purchase totals = $857.23       $956.2109   $956.22   $956.25   $956.10