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	$53.71	11.718%	$60.0037	$60.00	$60.00	$60.00
Purchase #2	$89.54	11.297%	$99.6553	$99.66	$99.65	$99.70
Purchase #3	$52.38	13.386%	$59.3916	$59.39	$59.40	$59.40
Purchase #4	$230.95	7.693%	$248.717	$248.72	$248.70	$248.70
Purchase #5	$109.86	5.438%	$115.8342	$115.83	$115.85	$115.80
Purchase #6	$103.28	3.127%	$106.5096	$106.51	$106.50	$106.50
Purchase #7	$100.50	13.162%	$113.7278	$113.73	$113.75	$113.70
7 purchase totals =	$740.22		$803.8392	$803.84	$803.85	$803.80