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 $24.27   8.581%   $26.3526   $26.35   $26.35   $26.40  
  Purchase #2 $112.73   9.627%   $123.5825   $123.58   $123.60   $123.60  
  Purchase #3 $244.45   9.147%   $266.8098   $266.81   $266.80   $266.80  
  Purchase #4 $233.62   6.499%   $248.803   $248.80   $248.80   $248.80  
  Purchase #5 $192.28   9.327%   $210.214   $210.21   $210.20   $210.20  
  Purchase #6 $196.91   11.431%   $219.4188   $219.42   $219.40   $219.40  
  Purchase #7 $124.87   3.256%   $128.9358   $128.94   $128.95   $128.90  
  7 purchase totals = $1,129.13       $1,224.1165   $1,224.11   $1,224.10   $1,224.10