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	$24.39	11.355%	$27.1595	$27.16	$27.15	$27.20
Purchase #2	$69.27	4.602%	$72.4578	$72.46	$72.45	$72.50
Purchase #3	$247.44	3.255%	$255.4942	$255.49	$255.50	$255.50
Purchase #4	$204.48	7.729%	$220.2843	$220.28	$220.30	$220.30
Purchase #5	$124.85	6.858%	$133.4122	$133.41	$133.40	$133.40
Purchase #6	$75.66	12.577%	$85.1758	$85.18	$85.20	$85.20
Purchase #7	$215.58	6.445%	$229.4741	$229.47	$229.45	$229.50
7 purchase totals =	$961.67		$1,023.4579	$1,023.45	$1,023.45	$1,023.60