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	$37.87	11.310%	$42.1531	$42.15	$42.15	$42.20
Purchase #2	$66.33	10.806%	$73.4976	$73.50	$73.50	$73.50
Purchase #3	$20.64	11.657%	$23.046	$23.05	$23.05	$23.00
Purchase #4	$37.31	5.124%	$39.2218	$39.22	$39.20	$39.20
Purchase #5	$120.59	8.171%	$130.4434	$130.44	$130.45	$130.40
Purchase #6	$101.32	3.693%	$105.0617	$105.06	$105.05	$105.10
Purchase #7	$245.44	9.743%	$269.3532	$269.35	$269.35	$269.40
7 purchase totals =	$629.50		$682.7768	$682.77	$682.75	$682.80