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	$182.48	5.276%	$192.1076	$192.11	$192.10	$192.10
Purchase #2	$198.88	12.234%	$223.211	$223.21	$223.20	$223.20
Purchase #3	$118.54	7.835%	$127.8276	$127.83	$127.85	$127.80
Purchase #4	$71.41	6.625%	$76.1409	$76.14	$76.15	$76.10
Purchase #5	$115.49	3.135%	$119.1106	$119.11	$119.10	$119.10
Purchase #6	$18.82	8.772%	$20.4709	$20.47	$20.45	$20.50
Purchase #7	$48.81	11.761%	$54.5505	$54.55	$54.55	$54.60
7 purchase totals =	$754.43		$813.4191	$813.42	$813.40	$813.40