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 $224.34   6.703%   $239.3775   $239.38   $239.40   $239.40  
  Purchase #2 $61.35   10.297%   $67.6672   $67.67   $67.65   $67.70  
  Purchase #3 $86.36   10.545%   $95.4667   $95.47   $95.45   $95.50  
  Purchase #4 $193.41   6.567%   $206.1112   $206.11   $206.10   $206.10  
  Purchase #5 $13.90   7.675%   $14.9668   $14.97   $14.95   $15.00  
  Purchase #6 $200.91   4.832%   $210.618   $210.62   $210.60   $210.60  
  Purchase #7 $182.69   8.643%   $198.4799   $198.48   $198.50   $198.50  
  7 purchase totals = $962.96       $1,032.6873   $1,032.70   $1,032.65   $1,032.80