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	$77.38	6.518%	$82.4236	$82.42	$82.40	$82.40
Purchase #2	$249.96	11.433%	$278.5379	$278.54	$278.55	$278.50
Purchase #3	$236.76	3.322%	$244.6252	$244.63	$244.65	$244.60
Purchase #4	$78.60	8.686%	$85.4272	$85.43	$85.45	$85.40
Purchase #5	$179.29	6.394%	$190.7538	$190.75	$190.75	$190.80
Purchase #6	$177.87	9.721%	$195.1607	$195.16	$195.15	$195.20
Purchase #7	$198.99	12.191%	$223.2489	$223.25	$223.25	$223.20
7 purchase totals =	$1,198.85		$1,300.1773	$1,300.18	$1,300.20	$1,300.10