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 $123.37   7.766%   $132.9509   $132.95   $132.95   $133.00  
  Purchase #2 $61.97   9.441%   $67.8206   $67.82   $67.80   $67.80  
  Purchase #3 $133.90   11.817%   $149.723   $149.72   $149.70   $149.70  
  Purchase #4 $171.55   12.724%   $193.378   $193.38   $193.40   $193.40  
  Purchase #5 $71.83   7.172%   $76.9816   $76.98   $77.00   $77.00  
  Purchase #6 $194.73   9.183%   $212.6121   $212.61   $212.60   $212.60  
  Purchase #7 $114.73   11.333%   $127.7324   $127.73   $127.75   $127.70  
  7 purchase totals = $872.08       $961.1986   $961.19   $961.20   $961.20