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 $246.56   12.601%   $277.629   $277.63   $277.65   $277.60  
  Purchase #2 $102.74   13.342%   $116.4476   $116.45   $116.45   $116.40  
  Purchase #3 $219.41   9.520%   $240.2978   $240.30   $240.30   $240.30  
  Purchase #4 $148.26   7.867%   $159.9236   $159.92   $159.90   $159.90  
  Purchase #5 $181.84   7.696%   $195.8344   $195.83   $195.85   $195.80  
  Purchase #6 $131.75   5.781%   $139.3665   $139.37   $139.35   $139.40  
  Purchase #7 $86.85   13.106%   $98.2326   $98.23   $98.25   $98.20  
  7 purchase totals = $1,117.41       $1,227.7315   $1,227.73   $1,227.75   $1,227.60