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 $64.45   4.852%   $67.5771   $67.58   $67.60   $67.60  
  Purchase #2 $75.47   13.195%   $85.4283   $85.43   $85.45   $85.40  
  Purchase #3 $83.75   11.219%   $93.1459   $93.15   $93.15   $93.10  
  Purchase #4 $176.44   4.730%   $184.7856   $184.79   $184.80   $184.80  
  Purchase #5 $132.35   6.651%   $141.1526   $141.15   $141.15   $141.20  
  Purchase #6 $233.35   10.238%   $257.2404   $257.24   $257.25   $257.20  
  Purchase #7 $65.51   11.415%   $72.988   $72.99   $73.00   $73.00  
  7 purchase totals = $831.32       $902.3179   $902.33   $902.40   $902.30