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 $238.27   8.254%   $257.9368   $257.94   $257.95   $257.90  
  Purchase #2 $216.74   4.371%   $226.2137   $226.21   $226.20   $226.20  
  Purchase #3 $108.55   9.797%   $119.1846   $119.18   $119.20   $119.20  
  Purchase #4 $101.87   10.655%   $112.7242   $112.72   $112.70   $112.70  
  Purchase #5 $114.85   8.860%   $125.0257   $125.03   $125.05   $125.00  
  Purchase #6 $158.93   6.638%   $169.4798   $169.48   $169.50   $169.50  
  Purchase #7 $19.80   8.729%   $21.5283   $21.53   $21.55   $21.50  
  7 purchase totals = $959.01       $1,032.0931   $1,032.09   $1,032.15   $1,032.00