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	$190.62	12.661%	$214.7544	$214.75	$214.75	$214.80
Purchase #2	$36.68	11.345%	$40.8413	$40.84	$40.85	$40.80
Purchase #3	$79.25	4.328%	$82.6799	$82.68	$82.70	$82.70
Purchase #4	$38.52	9.374%	$42.1309	$42.13	$42.15	$42.10
Purchase #5	$53.29	7.146%	$57.0981	$57.10	$57.10	$57.10
Purchase #6	$58.78	11.227%	$65.3792	$65.38	$65.40	$65.40
Purchase #7	$52.33	11.150%	$58.1648	$58.16	$58.15	$58.20
7 purchase totals =	$509.47		$561.0486	$561.04	$561.10	$561.10