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 $74.27   11.184%   $82.5764   $82.58   $82.60   $82.60  
  Purchase #2 $210.56   10.271%   $232.1866   $232.19   $232.20   $232.20  
  Purchase #3 $36.68   9.202%   $40.0553   $40.06   $40.05   $40.10  
  Purchase #4 $229.25   9.659%   $251.3933   $251.39   $251.40   $251.40  
  Purchase #5 $95.41   3.132%   $98.3982   $98.40   $98.40   $98.40  
  Purchase #6 $45.66   7.506%   $49.0872   $49.09   $49.10   $49.10  
  Purchase #7 $136.99   7.727%   $147.5752   $147.58   $147.60   $147.60  
  7 purchase totals = $828.82       $901.2722   $901.29   $901.35   $901.40