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	$250.79	7.380%	$269.2983	$269.30	$269.30	$269.30
Purchase #2	$227.96	11.238%	$253.5781	$253.58	$253.60	$253.60
Purchase #3	$58.81	11.592%	$65.6273	$65.63	$65.65	$65.60
Purchase #4	$118.26	12.800%	$133.3973	$133.40	$133.40	$133.40
Purchase #5	$132.65	10.454%	$146.5172	$146.52	$146.50	$146.50
Purchase #6	$66.60	6.816%	$71.1395	$71.14	$71.15	$71.10
Purchase #7	$123.54	6.596%	$131.6887	$131.69	$131.70	$131.70
7 purchase totals =	$978.61		$1,071.2464	$1,071.26	$1,071.30	$1,071.20