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 $185.26   11.856%   $207.2244   $207.22   $207.20   $207.20  
  Purchase #2 $72.90   9.476%   $79.808   $79.81   $79.80   $79.80  
  Purchase #3 $24.36   6.704%   $25.9931   $25.99   $26.00   $26.00  
  Purchase #4 $37.51   5.543%   $39.5892   $39.59   $39.60   $39.60  
  Purchase #5 $194.92   8.202%   $210.9073   $210.91   $210.90   $210.90  
  Purchase #6 $120.47   9.561%   $131.9881   $131.99   $132.00   $132.00  
  Purchase #7 $121.62   11.130%   $135.1563   $135.16   $135.15   $135.20  
  7 purchase totals = $757.04       $830.6664   $830.67   $830.65   $830.70