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 $86.31   13.843%   $98.2579   $98.26   $98.25   $98.30  
  Purchase #2 $206.55   7.607%   $222.2623   $222.26   $222.25   $222.30  
  Purchase #3 $26.95   11.228%   $29.9759   $29.98   $30.00   $30.00  
  Purchase #4 $79.77   6.867%   $85.2478   $85.25   $85.25   $85.20  
  Purchase #5 $220.41   7.254%   $236.3985   $236.40   $236.40   $236.40  
  Purchase #6 $57.36   12.771%   $64.6854   $64.69   $64.70   $64.70  
  Purchase #7 $13.29   8.347%   $14.3993   $14.40   $14.40   $14.40  
  7 purchase totals = $690.64       $751.2271   $751.24   $751.25   $751.30