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	$15.58	5.835%	$16.4891	$16.49	$16.50	$16.50
Purchase #2	$146.65	12.554%	$165.0604	$165.06	$165.05	$165.10
Purchase #3	$166.90	3.353%	$172.4962	$172.50	$172.50	$172.50
Purchase #4	$199.97	4.258%	$208.4847	$208.48	$208.50	$208.50
Purchase #5	$90.75	10.780%	$100.5329	$100.53	$100.55	$100.50
Purchase #6	$212.74	4.699%	$222.7367	$222.74	$222.75	$222.70
Purchase #7	$98.25	12.749%	$110.7759	$110.78	$110.80	$110.80
7 purchase totals =	$930.84		$996.5759	$996.58	$996.65	$996.60