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	$25.37	3.164%	$26.1727	$26.17	$26.15	$26.20
Purchase #2	$15.41	5.375%	$16.2383	$16.24	$16.25	$16.20
Purchase #3	$157.46	7.523%	$169.3057	$169.31	$169.30	$169.30
Purchase #4	$165.49	8.351%	$179.3101	$179.31	$179.30	$179.30
Purchase #5	$78.83	12.423%	$88.6231	$88.62	$88.60	$88.60
Purchase #6	$40.50	4.715%	$42.4096	$42.41	$42.40	$42.40
Purchase #7	$104.66	6.749%	$111.7235	$111.72	$111.70	$111.70
7 purchase totals =	$587.72		$633.7830	$633.78	$633.70	$633.70