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 $195.46   4.468%   $204.1932   $204.19   $204.20   $204.20  
  Purchase #2 $77.34   5.855%   $81.8683   $81.87   $81.85   $81.90  
  Purchase #3 $116.52   8.742%   $126.7062   $126.71   $126.70   $126.70  
  Purchase #4 $158.30   12.406%   $177.9387   $177.94   $177.95   $177.90  
  Purchase #5 $55.91   10.625%   $61.8504   $61.85   $61.85   $61.90  
  Purchase #6 $66.94   9.370%   $73.2123   $73.21   $73.20   $73.20  
  Purchase #7 $6.55   8.526%   $7.1085   $7.11   $7.10   $7.10  
  7 purchase totals = $677.02       $732.8776   $732.88   $732.85   $732.90