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	$197.98	12.483%	$222.6938	$222.69	$222.70	$222.70
Purchase #2	$56.49	5.259%	$59.4608	$59.46	$59.45	$59.50
Purchase #3	$221.38	6.603%	$235.9977	$236.00	$236.00	$236.00
Purchase #4	$172.72	10.374%	$190.638	$190.64	$190.65	$190.60
Purchase #5	$45.99	6.861%	$49.1454	$49.15	$49.15	$49.10
Purchase #6	$33.94	10.674%	$37.5628	$37.56	$37.55	$37.60
Purchase #7	$165.90	10.476%	$183.2797	$183.28	$183.30	$183.30
7 purchase totals =	$894.40		$978.7782	$978.78	$978.80	$978.80