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 $66.35   9.366%   $72.5643   $72.56   $72.55   $72.60  
  Purchase #2 $240.46   5.146%   $252.8341   $252.83   $252.85   $252.80  
  Purchase #3 $176.94   12.588%   $199.2132   $199.21   $199.20   $199.20  
  Purchase #4 $81.51   13.133%   $92.2147   $92.21   $92.20   $92.20  
  Purchase #5 $64.89   8.837%   $70.6243   $70.62   $70.60   $70.60  
  Purchase #6 $233.76   11.752%   $261.2315   $261.23   $261.25   $261.20  
  Purchase #7 $12.28   3.160%   $12.668   $12.67   $12.65   $12.70  
  7 purchase totals = $876.19       $961.3501   $961.33   $961.30   $961.30