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 $249.68   10.634%   $276.231   $276.23   $276.25   $276.20  
  Purchase #2 $106.89   11.258%   $118.9237   $118.92   $118.90   $118.90  
  Purchase #3 $245.94   3.827%   $255.3521   $255.35   $255.35   $255.40  
  Purchase #4 $233.60   7.359%   $250.7906   $250.79   $250.80   $250.80  
  Purchase #5 $200.70   6.253%   $213.2498   $213.25   $213.25   $213.20  
  Purchase #6 $165.50   8.585%   $179.7082   $179.71   $179.70   $179.70  
  Purchase #7 $199.86   9.198%   $218.2431   $218.24   $218.25   $218.20  
  7 purchase totals = $1,402.17       $1,512.4985   $1,512.49   $1,512.50   $1,512.40