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 $248.88   7.419%   $267.3444   $267.34   $267.35   $267.30  
  Purchase #2 $79.41   3.222%   $81.9686   $81.97   $81.95   $82.00  
  Purchase #3 $80.82   4.798%   $84.6977   $84.70   $84.70   $84.70  
  Purchase #4 $168.73   3.111%   $173.9792   $173.98   $174.00   $174.00  
  Purchase #5 $236.68   3.569%   $245.1271   $245.13   $245.15   $245.10  
  Purchase #6 $237.48   8.592%   $257.8843   $257.88   $257.90   $257.90  
  Purchase #7 $9.95   7.528%   $10.699   $10.70   $10.70   $10.70  
  7 purchase totals = $1,061.95       $1,121.7003   $1,121.70   $1,121.75   $1,121.70