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 $154.98   6.575%   $165.1699   $165.17   $165.15   $165.20  
  Purchase #2 $183.58   4.449%   $191.7475   $191.75   $191.75   $191.70  
  Purchase #3 $219.35   9.743%   $240.7213   $240.72   $240.70   $240.70  
  Purchase #4 $205.51   6.223%   $218.2989   $218.30   $218.30   $218.30  
  Purchase #5 $26.77   8.431%   $29.027   $29.03   $29.05   $29.00  
  Purchase #6 $126.30   3.471%   $130.6839   $130.68   $130.70   $130.70  
  Purchase #7 $44.25   13.271%   $50.1224   $50.12   $50.10   $50.10  
  7 purchase totals = $960.74       $1,025.7709   $1,025.77   $1,025.75   $1,025.70