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	$246.54	7.168%	$264.212	$264.21	$264.20	$264.20
Purchase #2	$53.86	9.771%	$59.1227	$59.12	$59.10	$59.10
Purchase #3	$190.47	3.495%	$197.1269	$197.13	$197.15	$197.10
Purchase #4	$169.36	10.663%	$187.4189	$187.42	$187.40	$187.40
Purchase #5	$116.64	9.358%	$127.5552	$127.56	$127.55	$127.60
Purchase #6	$11.76	6.181%	$12.4869	$12.49	$12.50	$12.50
Purchase #7	$66.48	6.629%	$70.887	$70.89	$70.90	$70.90
7 purchase totals =	$855.11		$918.8096	$918.82	$918.80	$918.80