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	$226.73	11.703%	$253.2642	$253.26	$253.25	$253.30
Purchase #2	$108.88	5.836%	$115.2342	$115.23	$115.25	$115.20
Purchase #3	$56.99	7.866%	$61.4728	$61.47	$61.45	$61.50
Purchase #4	$47.38	12.848%	$53.4674	$53.47	$53.45	$53.50
Purchase #5	$55.54	10.367%	$61.2978	$61.30	$61.30	$61.30
Purchase #6	$58.50	3.375%	$60.4744	$60.47	$60.45	$60.50
Purchase #7	$182.58	7.833%	$196.8815	$196.88	$196.90	$196.90
7 purchase totals =	$736.60		$802.0923	$802.08	$802.05	$802.20