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	$159.45	9.125%	$173.9998	$174.00	$174.00	$174.00
Purchase #2	$146.55	13.105%	$165.7554	$165.76	$165.75	$165.80
Purchase #3	$6.56	12.595%	$7.3862	$7.39	$7.40	$7.40
Purchase #4	$141.28	8.138%	$152.7774	$152.78	$152.80	$152.80
Purchase #5	$37.49	8.744%	$40.7681	$40.77	$40.75	$40.80
Purchase #6	$80.83	12.705%	$91.0995	$91.10	$91.10	$91.10
Purchase #7	$13.91	6.329%	$14.7904	$14.79	$14.80	$14.80
7 purchase totals =	$586.07		$646.5768	$646.59	$646.60	$646.70