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	$20.55	5.468%	$21.6737	$21.67	$21.65	$21.70
Purchase #2	$149.57	10.442%	$165.1881	$165.19	$165.20	$165.20
Purchase #3	$107.66	10.118%	$118.553	$118.55	$118.55	$118.60
Purchase #4	$135.85	12.453%	$152.7674	$152.77	$152.75	$152.80
Purchase #5	$148.88	5.461%	$157.0103	$157.01	$157.00	$157.00
Purchase #6	$142.61	13.632%	$162.0506	$162.05	$162.05	$162.10
Purchase #7	$72.59	7.855%	$78.2919	$78.29	$78.30	$78.30
7 purchase totals =	$777.71		$855.5350	$855.53	$855.50	$855.70