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	$19.32	7.266%	$20.7238	$20.72	$20.70	$20.70
Purchase #2	$50.88	4.512%	$53.1757	$53.18	$53.20	$53.20
Purchase #3	$209.82	10.337%	$231.5091	$231.51	$231.50	$231.50
Purchase #4	$196.87	9.346%	$215.2695	$215.27	$215.25	$215.30
Purchase #5	$141.31	8.696%	$153.5983	$153.60	$153.60	$153.60
Purchase #6	$180.51	9.285%	$197.2704	$197.27	$197.25	$197.30
Purchase #7	$204.83	13.114%	$231.6914	$231.69	$231.70	$231.70
7 purchase totals =	$1,003.54		$1,103.2382	$1,103.24	$1,103.20	$1,103.30