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 $229.54   8.480%   $249.005   $249.01   $249.00   $249.00  
  Purchase #2 $112.91   5.315%   $118.9112   $118.91   $118.90   $118.90  
  Purchase #3 $141.33   11.577%   $157.6918   $157.69   $157.70   $157.70  
  Purchase #4 $92.45   12.372%   $103.8879   $103.89   $103.90   $103.90  
  Purchase #5 $169.74   7.473%   $182.4247   $182.42   $182.40   $182.40  
  Purchase #6 $63.54   7.337%   $68.2019   $68.20   $68.20   $68.20  
  Purchase #7 $139.27   10.328%   $153.6538   $153.65   $153.65   $153.70  
  7 purchase totals = $948.78       $1,033.7763   $1,033.77   $1,033.75   $1,033.80