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 $233.32   9.279%   $254.9698   $254.97   $254.95   $255.00  
  Purchase #2 $53.34   6.374%   $56.7399   $56.74   $56.75   $56.70  
  Purchase #3 $5.83   4.667%   $6.1021   $6.10   $6.10   $6.10  
  Purchase #4 $87.47   7.139%   $93.7145   $93.71   $93.70   $93.70  
  Purchase #5 $182.71   3.742%   $189.547   $189.55   $189.55   $189.50  
  Purchase #6 $247.47   5.215%   $260.3756   $260.38   $260.40   $260.40  
  Purchase #7 $12.73   10.407%   $14.0548   $14.05   $14.05   $14.10  
  7 purchase totals = $822.87       $875.5037   $875.50   $875.50   $875.50