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 $113.79   3.138%   $117.3607   $117.36   $117.35   $117.40  
  Purchase #2 $50.94   12.577%   $57.3467   $57.35   $57.35   $57.30  
  Purchase #3 $58.64   9.382%   $64.1416   $64.14   $64.15   $64.10  
  Purchase #4 $91.41   7.347%   $98.1259   $98.13   $98.15   $98.10  
  Purchase #5 $235.62   10.210%   $259.6768   $259.68   $259.70   $259.70  
  Purchase #6 $112.94   4.481%   $118.0008   $118.00   $118.00   $118.00  
  Purchase #7 $66.73   10.343%   $73.6319   $73.63   $73.65   $73.60  
  7 purchase totals = $730.07       $788.2844   $788.29   $788.35   $788.20