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   4.196%   $63.2157   $63.22   $63.20   $63.20  
  Purchase #2 $132.84   10.614%   $146.9396   $146.94   $146.95   $146.90  
  Purchase #3 $10.79   8.851%   $11.745   $11.75   $11.75   $11.70  
  Purchase #4 $205.36   8.689%   $223.2037   $223.20   $223.20   $223.20  
  Purchase #5 $63.85   12.271%   $71.685   $71.69   $71.70   $71.70  
  Purchase #6 $93.30   8.841%   $101.5487   $101.55   $101.55   $101.50  
  Purchase #7 $245.45   6.266%   $260.8299   $260.83   $260.85   $260.80  
  7 purchase totals = $812.26       $879.1676   $879.18   $879.20   $879.00