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	$247.47	7.185%	$265.2507	$265.25	$265.25	$265.30
Purchase #2	$36.52	13.608%	$41.4896	$41.49	$41.50	$41.50
Purchase #3	$45.96	9.502%	$50.3271	$50.33	$50.35	$50.30
Purchase #4	$140.70	3.657%	$145.8454	$145.85	$145.85	$145.80
Purchase #5	$225.80	4.428%	$235.7984	$235.80	$235.80	$235.80
Purchase #6	$161.81	3.605%	$167.6433	$167.64	$167.65	$167.60
Purchase #7	$66.35	8.386%	$71.9141	$71.91	$71.90	$71.90
7 purchase totals =	$924.61		$978.2686	$978.27	$978.30	$978.20