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	$71.33	4.447%	$74.502	$74.50	$74.50	$74.50
Purchase #2	$50.75	7.126%	$54.3664	$54.37	$54.35	$54.40
Purchase #3	$10.94	7.511%	$11.7617	$11.76	$11.75	$11.80
Purchase #4	$209.25	6.152%	$222.1231	$222.12	$222.10	$222.10
Purchase #5	$178.97	3.426%	$185.1015	$185.10	$185.10	$185.10
Purchase #6	$190.88	5.155%	$200.7199	$200.72	$200.70	$200.70
Purchase #7	$160.40	7.128%	$171.8333	$171.83	$171.85	$171.80
7 purchase totals =	$872.52		$920.4079	$920.40	$920.35	$920.40