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	$51.83	3.185%	$53.4808	$53.48	$53.50	$53.50
Purchase #2	$135.69	11.394%	$151.1505	$151.15	$151.15	$151.20
Purchase #3	$120.70	4.817%	$126.5141	$126.51	$126.50	$126.50
Purchase #4	$138.33	7.228%	$148.3285	$148.33	$148.35	$148.30
Purchase #5	$198.48	8.237%	$214.8288	$214.83	$214.85	$214.80
Purchase #6	$196.58	9.444%	$215.145	$215.15	$215.15	$215.10
Purchase #7	$43.69	11.644%	$48.7773	$48.78	$48.80	$48.80
7 purchase totals =	$885.30		$958.2250	$958.23	$958.30	$958.20