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 $113.56   11.177%   $126.2526   $126.25   $126.25   $126.30  
  Purchase #2 $151.66   10.230%   $167.1748   $167.17   $167.15   $167.20  
  Purchase #3 $29.33   9.552%   $32.1316   $32.13   $32.15   $32.10  
  Purchase #4 $203.58   6.405%   $216.6193   $216.62   $216.60   $216.60  
  Purchase #5 $22.68   11.834%   $25.364   $25.36   $25.35   $25.40  
  Purchase #6 $21.64   8.176%   $23.4093   $23.41   $23.40   $23.40  
  Purchase #7 $29.57   9.795%   $32.4664   $32.47   $32.45   $32.50  
  7 purchase totals = $572.02       $623.4180   $623.41   $623.35   $623.50