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 $246.53   11.379%   $274.5826   $274.58   $274.60   $274.60  
  Purchase #2 $122.84   11.697%   $137.2086   $137.21   $137.20   $137.20  
  Purchase #3 $185.99   6.438%   $197.964   $197.96   $197.95   $198.00  
  Purchase #4 $114.28   10.646%   $126.4462   $126.45   $126.45   $126.40  
  Purchase #5 $209.28   8.294%   $226.6377   $226.64   $226.65   $226.60  
  Purchase #6 $225.50   4.161%   $234.8831   $234.88   $234.90   $234.90  
  Purchase #7 $13.56   13.410%   $15.3784   $15.38   $15.40   $15.40  
  7 purchase totals = $1,117.98       $1,213.1006   $1,213.10   $1,213.15   $1,213.10