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 $248.54   9.712%   $272.6782   $272.68   $272.70   $272.70  
  Purchase #2 $10.35   6.401%   $11.0125   $11.01   $11.00   $11.00  
  Purchase #3 $52.63   10.792%   $58.3098   $58.31   $58.30   $58.30  
  Purchase #4 $218.28   4.450%   $227.9935   $227.99   $228.00   $228.00  
  Purchase #5 $112.41   11.736%   $125.6024   $125.60   $125.60   $125.60  
  Purchase #6 $169.72   4.221%   $176.8839   $176.88   $176.90   $176.90  
  Purchase #7 $136.50   11.566%   $152.2876   $152.29   $152.30   $152.30  
  7 purchase totals = $948.43       $1,024.7679   $1,024.76   $1,024.80   $1,024.80