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	$99.90	3.134%	$103.0309	$103.03	$103.05	$103.00
Purchase #2	$129.30	5.519%	$136.4361	$136.44	$136.45	$136.40
Purchase #3	$67.78	4.397%	$70.7603	$70.76	$70.75	$70.80
Purchase #4	$128.26	8.539%	$139.2121	$139.21	$139.20	$139.20
Purchase #5	$16.64	11.663%	$18.5807	$18.58	$18.60	$18.60
Purchase #6	$37.52	13.353%	$42.53	$42.53	$42.55	$42.50
Purchase #7	$135.98	5.631%	$143.637	$143.64	$143.65	$143.60
7 purchase totals =	$615.38		$654.1871	$654.19	$654.25	$654.10