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 $46.52   3.333%   $48.0705   $48.07   $48.05   $48.10  
  Purchase #2 $183.41   7.694%   $197.5216   $197.52   $197.50   $197.50  
  Purchase #3 $51.37   8.832%   $55.907   $55.91   $55.90   $55.90  
  Purchase #4 $214.45   3.234%   $221.3853   $221.39   $221.40   $221.40  
  Purchase #5 $85.88   8.821%   $93.4555   $93.46   $93.45   $93.50  
  Purchase #6 $146.89   11.304%   $163.4944   $163.49   $163.50   $163.50  
  Purchase #7 $35.66   7.858%   $38.4622   $38.46   $38.45   $38.50  
  7 purchase totals = $764.18       $818.2965   $818.30   $818.25   $818.40