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 $59.47   5.511%   $62.7474   $62.75   $62.75   $62.70  
  Purchase #2 $86.46   12.806%   $97.5321   $97.53   $97.55   $97.50  
  Purchase #3 $73.28   7.264%   $78.6031   $78.60   $78.60   $78.60  
  Purchase #4 $49.85   3.786%   $51.7373   $51.74   $51.75   $51.70  
  Purchase #5 $134.87   10.822%   $149.4656   $149.47   $149.45   $149.50  
  Purchase #6 $89.90   3.447%   $92.9989   $93.00   $93.00   $93.00  
  Purchase #7 $34.26   8.248%   $37.0858   $37.09   $37.10   $37.10  
  7 purchase totals = $528.09       $570.1702   $570.18   $570.20   $570.10