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 $73.38   11.694%   $81.9611   $81.96   $81.95   $82.00  
  Purchase #2 $109.87   5.741%   $116.1776   $116.18   $116.20   $116.20  
  Purchase #3 $201.45   13.195%   $228.0313   $228.03   $228.05   $228.00  
  Purchase #4 $145.35   11.165%   $161.5783   $161.58   $161.60   $161.60  
  Purchase #5 $241.86   5.557%   $255.3002   $255.30   $255.30   $255.30  
  Purchase #6 $136.48   6.330%   $145.1192   $145.12   $145.10   $145.10  
  Purchase #7 $81.92   5.461%   $86.3937   $86.39   $86.40   $86.40  
  7 purchase totals = $990.31       $1,074.5614   $1,074.56   $1,074.60   $1,074.60