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	$63.61	5.813%	$67.3076	$67.31	$67.30	$67.30
Purchase #2	$146.57	6.791%	$156.5236	$156.52	$156.50	$156.50
Purchase #3	$79.56	13.443%	$90.2553	$90.26	$90.25	$90.30
Purchase #4	$170.48	11.240%	$189.642	$189.64	$189.65	$189.60
Purchase #5	$77.56	8.495%	$84.1487	$84.15	$84.15	$84.10
Purchase #6	$49.92	9.414%	$54.6195	$54.62	$54.60	$54.60
Purchase #7	$54.48	4.663%	$57.0204	$57.02	$57.00	$57.00
7 purchase totals =	$642.18		$699.5171	$699.52	$699.45	$699.40