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 $245.37   7.692%   $264.2439   $264.24   $264.25   $264.20  
  Purchase #2 $230.29   10.848%   $255.2719   $255.27   $255.25   $255.30  
  Purchase #3 $64.89   7.686%   $69.8774   $69.88   $69.90   $69.90  
  Purchase #4 $248.40   10.397%   $274.2261   $274.23   $274.25   $274.20  
  Purchase #5 $61.85   4.671%   $64.739   $64.74   $64.75   $64.70  
  Purchase #6 $104.56   5.316%   $110.1184   $110.12   $110.10   $110.10  
  Purchase #7 $24.59   8.707%   $26.7311   $26.73   $26.75   $26.70  
  7 purchase totals = $979.95       $1,065.2078   $1,065.21   $1,065.25   $1,065.10