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 $100.42   12.124%   $112.5949   $112.59   $112.60   $112.60  
  Purchase #2 $102.69   3.235%   $106.012   $106.01   $106.00   $106.00  
  Purchase #3 $76.77   3.207%   $79.232   $79.23   $79.25   $79.20  
  Purchase #4 $155.25   11.741%   $173.4779   $173.48   $173.50   $173.50  
  Purchase #5 $45.79   11.375%   $50.9986   $51.00   $51.00   $51.00  
  Purchase #6 $15.41   13.688%   $17.5193   $17.52   $17.50   $17.50  
  Purchase #7 $115.59   3.586%   $119.7351   $119.74   $119.75   $119.70  
  7 purchase totals = $611.92       $659.5698   $659.57   $659.60   $659.50