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	$37.47	12.799%	$42.2658	$42.27	$42.25	$42.30
Purchase #2	$155.72	12.822%	$175.6864	$175.69	$175.70	$175.70
Purchase #3	$108.47	5.350%	$114.2731	$114.27	$114.25	$114.30
Purchase #4	$219.45	8.685%	$238.5092	$238.51	$238.50	$238.50
Purchase #5	$100.30	13.826%	$114.1675	$114.17	$114.15	$114.20
Purchase #6	$122.97	11.506%	$137.1189	$137.12	$137.10	$137.10
Purchase #7	$129.96	5.686%	$137.3495	$137.35	$137.35	$137.30
7 purchase totals =	$874.34		$959.3704	$959.38	$959.30	$959.40