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 $59.82   11.366%   $66.6191   $66.62   $66.60   $66.60  
  Purchase #2 $151.56   9.351%   $165.7324   $165.73   $165.75   $165.70  
  Purchase #3 $22.72   12.642%   $25.5923   $25.59   $25.60   $25.60  
  Purchase #4 $18.28   10.475%   $20.1948   $20.19   $20.20   $20.20  
  Purchase #5 $18.38   3.333%   $18.9926   $18.99   $19.00   $19.00  
  Purchase #6 $174.79   13.556%   $198.4845   $198.48   $198.50   $198.50  
  Purchase #7 $66.27   3.532%   $68.6107   $68.61   $68.60   $68.60  
  7 purchase totals = $511.82       $564.2264   $564.21   $564.25   $564.20