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 $44.37   8.821%   $48.2839   $48.28   $48.30   $48.30  
  Purchase #2 $110.84   13.253%   $125.5296   $125.53   $125.55   $125.50  
  Purchase #3 $245.29   9.466%   $268.5092   $268.51   $268.50   $268.50  
  Purchase #4 $142.25   13.283%   $161.1451   $161.15   $161.15   $161.10  
  Purchase #5 $61.57   8.720%   $66.9389   $66.94   $66.95   $66.90  
  Purchase #6 $77.52   3.418%   $80.1696   $80.17   $80.15   $80.20  
  Purchase #7 $13.66   9.837%   $15.0037   $15.00   $15.00   $15.00  
  7 purchase totals = $695.50       $765.5800   $765.58   $765.60   $765.50