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	$161.40	12.591%	$181.7219	$181.72	$181.70	$181.70
Purchase #2	$157.97	11.168%	$175.6121	$175.61	$175.60	$175.60
Purchase #3	$81.62	5.793%	$86.3482	$86.35	$86.35	$86.30
Purchase #4	$30.79	3.549%	$31.8827	$31.88	$31.90	$31.90
Purchase #5	$80.87	12.404%	$90.9011	$90.90	$90.90	$90.90
Purchase #6	$151.64	5.158%	$159.4616	$159.46	$159.45	$159.50
Purchase #7	$154.48	13.485%	$175.3116	$175.31	$175.30	$175.30
7 purchase totals =	$818.77		$901.2392	$901.23	$901.20	$901.20