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 $246.68   5.862%   $261.1404   $261.14   $261.15   $261.10  
  Purchase #2 $137.57   13.830%   $156.5959   $156.60   $156.60   $156.60  
  Purchase #3 $141.28   7.149%   $151.3801   $151.38   $151.40   $151.40  
  Purchase #4 $16.72   5.664%   $17.667   $17.67   $17.65   $17.70  
  Purchase #5 $151.70   11.521%   $169.1774   $169.18   $169.20   $169.20  
  Purchase #6 $53.94   8.375%   $58.4575   $58.46   $58.45   $58.50  
  Purchase #7 $218.85   9.106%   $238.7785   $238.78   $238.80   $238.80  
  7 purchase totals = $966.74       $1,053.1968   $1,053.21   $1,053.25   $1,053.30