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	$239.72	13.565%	$272.238	$272.24	$272.25	$272.20
Purchase #2	$113.42	3.666%	$117.578	$117.58	$117.60	$117.60
Purchase #3	$182.85	7.552%	$196.6588	$196.66	$196.65	$196.70
Purchase #4	$249.58	13.181%	$282.4771	$282.48	$282.50	$282.50
Purchase #5	$120.73	6.608%	$128.7078	$128.71	$128.70	$128.70
Purchase #6	$77.75	9.735%	$85.319	$85.32	$85.30	$85.30
Purchase #7	$226.55	7.865%	$244.3682	$244.37	$244.35	$244.40
7 purchase totals =	$1,210.60		$1,327.3469	$1,327.36	$1,327.35	$1,327.40