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	$24.64	9.191%	$26.9047	$26.90	$26.90	$26.90
Purchase #2	$170.86	13.235%	$193.4733	$193.47	$193.45	$193.50
Purchase #3	$155.50	3.407%	$160.7979	$160.80	$160.80	$160.80
Purchase #4	$182.56	4.400%	$190.5926	$190.59	$190.60	$190.60
Purchase #5	$196.64	9.663%	$215.6413	$215.64	$215.65	$215.60
Purchase #6	$208.52	9.574%	$228.4837	$228.48	$228.50	$228.50
Purchase #7	$145.74	4.366%	$152.103	$152.10	$152.10	$152.10
7 purchase totals =	$1,084.46		$1,167.9965	$1,167.98	$1,168.00	$1,168.00