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	$70.61	13.821%	$80.369	$80.37	$80.35	$80.40
Purchase #2	$168.41	6.602%	$179.5284	$179.53	$179.55	$179.50
Purchase #3	$182.57	4.485%	$190.7583	$190.76	$190.75	$190.80
Purchase #4	$142.49	12.413%	$160.1773	$160.18	$160.20	$160.20
Purchase #5	$234.78	6.385%	$249.7707	$249.77	$249.75	$249.80
Purchase #6	$163.39	5.418%	$172.2425	$172.24	$172.25	$172.20
Purchase #7	$102.58	8.414%	$111.2111	$111.21	$111.20	$111.20
7 purchase totals =	$1,064.83		$1,144.0573	$1,144.06	$1,144.05	$1,144.10