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	$130.98	7.644%	$140.9921	$140.99	$141.00	$141.00
Purchase #2	$46.48	6.410%	$49.4594	$49.46	$49.45	$49.50
Purchase #3	$157.73	13.601%	$179.1829	$179.18	$179.20	$179.20
Purchase #4	$115.51	10.497%	$127.6351	$127.64	$127.65	$127.60
Purchase #5	$128.37	13.655%	$145.8989	$145.90	$145.90	$145.90
Purchase #6	$135.40	11.739%	$151.2946	$151.29	$151.30	$151.30
Purchase #7	$53.30	3.613%	$55.2257	$55.23	$55.25	$55.20
7 purchase totals =	$767.77		$849.6887	$849.69	$849.75	$849.70