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	$97.89	3.138%	$100.9618	$100.96	$100.95	$101.00
Purchase #2	$179.30	10.467%	$198.0673	$198.07	$198.05	$198.10
Purchase #3	$142.91	10.391%	$157.7598	$157.76	$157.75	$157.80
Purchase #4	$21.39	4.196%	$22.2875	$22.29	$22.30	$22.30
Purchase #5	$141.65	12.566%	$159.4497	$159.45	$159.45	$159.40
Purchase #6	$187.84	4.596%	$196.4731	$196.47	$196.45	$196.50
Purchase #7	$38.26	11.444%	$42.6385	$42.64	$42.65	$42.60
7 purchase totals =	$809.24		$877.6377	$877.64	$877.60	$877.70