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 $85.85   7.531%   $92.3154   $92.32   $92.30   $92.30  
  Purchase #2 $182.42   8.566%   $198.0461   $198.05   $198.05   $198.00  
  Purchase #3 $6.28   6.439%   $6.6844   $6.68   $6.70   $6.70  
  Purchase #4 $30.86   12.544%   $34.7311   $34.73   $34.75   $34.70  
  Purchase #5 $62.85   6.822%   $67.1376   $67.14   $67.15   $67.10  
  Purchase #6 $248.73   13.332%   $281.8907   $281.89   $281.90   $281.90  
  Purchase #7 $73.83   12.283%   $82.8985   $82.90   $82.90   $82.90  
  7 purchase totals = $690.82       $763.7038   $763.71   $763.75   $763.60