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 $46.88   6.129%   $49.7533   $49.75   $49.75   $49.80  
  Purchase #2 $227.47   4.566%   $237.8563   $237.86   $237.85   $237.90  
  Purchase #3 $62.38   5.800%   $65.998   $66.00   $66.00   $66.00  
  Purchase #4 $95.48   7.222%   $102.3756   $102.38   $102.40   $102.40  
  Purchase #5 $10.72   13.159%   $12.1306   $12.13   $12.15   $12.10  
  Purchase #6 $11.31   10.370%   $12.4828   $12.48   $12.50   $12.50  
  Purchase #7 $210.72   12.367%   $236.7797   $236.78   $236.80   $236.80  
  7 purchase totals = $664.96       $717.3763   $717.38   $717.45   $717.50