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 $119.62   3.799%   $124.1644   $124.16   $124.15   $124.20  
  Purchase #2 $62.73   6.669%   $66.9135   $66.91   $66.90   $66.90  
  Purchase #3 $135.75   4.603%   $141.9986   $142.00   $142.00   $142.00  
  Purchase #4 $98.39   9.694%   $107.9279   $107.93   $107.95   $107.90  
  Purchase #5 $118.99   11.694%   $132.9047   $132.90   $132.90   $132.90  
  Purchase #6 $209.30   10.611%   $231.5088   $231.51   $231.50   $231.50  
  Purchase #7 $233.33   10.481%   $257.7853   $257.79   $257.80   $257.80  
  7 purchase totals = $978.11       $1,063.2032   $1,063.20   $1,063.20   $1,063.20