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	$34.52	7.798%	$37.2119	$37.21	$37.20	$37.20
Purchase #2	$76.46	8.276%	$82.7878	$82.79	$82.80	$82.80
Purchase #3	$237.85	9.639%	$260.7764	$260.78	$260.80	$260.80
Purchase #4	$74.32	5.268%	$78.2352	$78.24	$78.25	$78.20
Purchase #5	$98.83	4.503%	$103.2803	$103.28	$103.30	$103.30
Purchase #6	$242.83	13.103%	$274.648	$274.65	$274.65	$274.60
Purchase #7	$198.46	4.511%	$207.4125	$207.41	$207.40	$207.40
7 purchase totals =	$963.27		$1,044.3521	$1,044.36	$1,044.40	$1,044.30