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 $34.72   11.605%   $38.7493   $38.75   $38.75   $38.70  
  Purchase #2 $186.29   7.278%   $199.8482   $199.85   $199.85   $199.80  
  Purchase #3 $157.27   11.747%   $175.7445   $175.74   $175.75   $175.70  
  Purchase #4 $213.38   13.770%   $242.7624   $242.76   $242.75   $242.80  
  Purchase #5 $101.40   12.600%   $114.1764   $114.18   $114.20   $114.20  
  Purchase #6 $144.61   10.781%   $160.2004   $160.20   $160.20   $160.20  
  Purchase #7 $92.48   6.359%   $98.3608   $98.36   $98.35   $98.40  
  7 purchase totals = $930.15       $1,029.8420   $1,029.84   $1,029.85   $1,029.80