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	$59.35	11.597%	$66.2328	$66.23	$66.25	$66.20
Purchase #2	$78.61	7.483%	$84.4924	$84.49	$84.50	$84.50
Purchase #3	$145.45	4.173%	$151.5196	$151.52	$151.50	$151.50
Purchase #4	$37.40	10.312%	$41.2567	$41.26	$41.25	$41.30
Purchase #5	$45.52	10.329%	$50.2218	$50.22	$50.20	$50.20
Purchase #6	$104.88	4.306%	$109.3961	$109.40	$109.40	$109.40
Purchase #7	$124.40	13.760%	$141.5174	$141.52	$141.50	$141.50
7 purchase totals =	$595.61		$644.6368	$644.64	$644.60	$644.60