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 $83.95   13.548%   $95.3235   $95.32   $95.30   $95.30  
  Purchase #2 $23.32   5.566%   $24.618   $24.62   $24.60   $24.60  
  Purchase #3 $171.95   7.619%   $185.0509   $185.05   $185.05   $185.10  
  Purchase #4 $116.92   8.863%   $127.2826   $127.28   $127.30   $127.30  
  Purchase #5 $84.86   8.738%   $92.2751   $92.28   $92.30   $92.30  
  Purchase #6 $148.33   6.116%   $157.4019   $157.40   $157.40   $157.40  
  Purchase #7 $158.29   8.306%   $171.4376   $171.44   $171.45   $171.40  
  7 purchase totals = $787.62       $853.3896   $853.39   $853.40   $853.40