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 $16.42   3.532%   $17   $17.00   $17.00   $17.00  
  Purchase #2 $244.86   9.220%   $267.4361   $267.44   $267.45   $267.40  
  Purchase #3 $183.65   6.536%   $195.6534   $195.65   $195.65   $195.70  
  Purchase #4 $241.60   8.234%   $261.4933   $261.49   $261.50   $261.50  
  Purchase #5 $222.41   3.702%   $230.6436   $230.64   $230.65   $230.60  
  Purchase #6 $118.48   11.433%   $132.0258   $132.03   $132.05   $132.00  
  Purchase #7 $117.99   10.349%   $130.2008   $130.20   $130.20   $130.20  
  7 purchase totals = $1,145.41       $1,234.4530   $1,234.45   $1,234.50   $1,234.40