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	$39.53	7.763%	$42.5987	$42.60	$42.60	$42.60
Purchase #2	$67.72	4.469%	$70.7464	$70.75	$70.75	$70.70
Purchase #3	$12.57	8.772%	$13.6726	$13.67	$13.65	$13.70
Purchase #4	$170.56	8.592%	$185.2145	$185.21	$185.20	$185.20
Purchase #5	$200.77	6.279%	$213.3763	$213.38	$213.40	$213.40
Purchase #6	$92.50	6.362%	$98.3849	$98.38	$98.40	$98.40
Purchase #7	$18.59	9.105%	$20.2826	$20.28	$20.30	$20.30
7 purchase totals =	$602.24		$644.2760	$644.27	$644.30	$644.30