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 $113.35   9.812%   $124.4719   $124.47   $124.45   $124.50  
  Purchase #2 $207.98   6.625%   $221.7587   $221.76   $221.75   $221.80  
  Purchase #3 $32.60   3.535%   $33.7524   $33.75   $33.75   $33.80  
  Purchase #4 $192.93   6.461%   $205.3952   $205.40   $205.40   $205.40  
  Purchase #5 $86.91   8.384%   $94.1965   $94.20   $94.20   $94.20  
  Purchase #6 $116.64   13.485%   $132.3689   $132.37   $132.35   $132.40  
  Purchase #7 $247.49   13.675%   $281.3343   $281.33   $281.35   $281.30  
  7 purchase totals = $997.90       $1,093.2779   $1,093.28   $1,093.25   $1,093.40