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 $60.67   11.576%   $67.6932   $67.69   $67.70   $67.70  
  Purchase #2 $122.37   8.646%   $132.9501   $132.95   $132.95   $133.00  
  Purchase #3 $188.76   5.159%   $198.4981   $198.50   $198.50   $198.50  
  Purchase #4 $15.64   12.530%   $17.5997   $17.60   $17.60   $17.60  
  Purchase #5 $119.74   11.777%   $133.8418   $133.84   $133.85   $133.80  
  Purchase #6 $191.27   5.136%   $201.0936   $201.09   $201.10   $201.10  
  Purchase #7 $203.93   5.468%   $215.0809   $215.08   $215.10   $215.10  
  7 purchase totals = $902.38       $966.7574   $966.75   $966.80   $966.80