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 $244.81   13.283%   $277.3281   $277.33   $277.35   $277.30  
  Purchase #2 $110.64   7.853%   $119.3286   $119.33   $119.35   $119.30  
  Purchase #3 $129.79   4.238%   $135.2905   $135.29   $135.30   $135.30  
  Purchase #4 $216.37   11.541%   $241.3413   $241.34   $241.35   $241.30  
  Purchase #5 $109.60   5.271%   $115.377   $115.38   $115.40   $115.40  
  Purchase #6 $178.75   8.391%   $193.7489   $193.75   $193.75   $193.70  
  Purchase #7 $240.56   9.707%   $263.9112   $263.91   $263.90   $263.90  
  7 purchase totals = $1,230.52       $1,346.3256   $1,346.33   $1,346.40   $1,346.20