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	$53.66	6.842%	$57.3314	$57.33	$57.35	$57.30
Purchase #2	$152.61	9.751%	$167.491	$167.49	$167.50	$167.50
Purchase #3	$97.82	8.834%	$106.4614	$106.46	$106.45	$106.50
Purchase #4	$177.70	7.248%	$190.5797	$190.58	$190.60	$190.60
Purchase #5	$168.38	13.520%	$191.145	$191.15	$191.15	$191.10
Purchase #6	$158.28	7.503%	$170.1557	$170.16	$170.15	$170.20
Purchase #7	$232.27	10.150%	$255.8454	$255.85	$255.85	$255.80
7 purchase totals =	$1,040.72		$1,139.0096	$1,139.02	$1,139.05	$1,139.00