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 $221.43   11.658%   $247.2443   $247.24   $247.25   $247.20  
  Purchase #2 $94.81   7.535%   $101.9539   $101.95   $101.95   $102.00  
  Purchase #3 $53.59   11.855%   $59.9431   $59.94   $59.95   $59.90  
  Purchase #4 $123.62   11.597%   $137.9562   $137.96   $137.95   $138.00  
  Purchase #5 $15.41   10.170%   $16.9772   $16.98   $17.00   $17.00  
  Purchase #6 $106.94   11.524%   $119.2638   $119.26   $119.25   $119.30  
  Purchase #7 $161.84   10.657%   $179.0873   $179.09   $179.10   $179.10  
  7 purchase totals = $777.64       $862.4258   $862.42   $862.45   $862.50