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	$78.89	6.187%	$83.7709	$83.77	$83.75	$83.80
Purchase #2	$200.64	11.446%	$223.6053	$223.61	$223.60	$223.60
Purchase #3	$133.52	9.778%	$146.5756	$146.58	$146.60	$146.60
Purchase #4	$166.94	4.324%	$174.1585	$174.16	$174.15	$174.20
Purchase #5	$151.87	8.444%	$164.6939	$164.69	$164.70	$164.70
Purchase #6	$84.91	5.478%	$89.5614	$89.56	$89.55	$89.60
Purchase #7	$64.46	7.282%	$69.154	$69.15	$69.15	$69.20
7 purchase totals =	$881.23		$951.5196	$951.52	$951.50	$951.70