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 $138.34   9.162%   $151.0147   $151.01   $151.00   $151.00  
  Purchase #2 $176.71   10.324%   $194.9535   $194.95   $194.95   $195.00  
  Purchase #3 $79.31   5.230%   $83.4579   $83.46   $83.45   $83.50  
  Purchase #4 $201.50   5.463%   $212.5079   $212.51   $212.50   $212.50  
  Purchase #5 $61.73   9.771%   $67.7616   $67.76   $67.75   $67.80  
  Purchase #6 $241.45   13.601%   $274.2896   $274.29   $274.30   $274.30  
  Purchase #7 $249.33   11.510%   $278.0279   $278.03   $278.05   $278.00  
  7 purchase totals = $1,148.37       $1,262.0131   $1,262.01   $1,262.00   $1,262.10