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	$25.47	11.715%	$28.4538	$28.45	$28.45	$28.50
Purchase #2	$188.46	12.340%	$211.716	$211.72	$211.70	$211.70
Purchase #3	$221.75	8.755%	$241.1642	$241.16	$241.15	$241.20
Purchase #4	$16.64	12.518%	$18.723	$18.72	$18.70	$18.70
Purchase #5	$19.74	5.576%	$20.8407	$20.84	$20.85	$20.80
Purchase #6	$159.61	9.643%	$175.0012	$175.00	$175.00	$175.00
Purchase #7	$57.25	4.682%	$59.9304	$59.93	$59.95	$59.90
7 purchase totals =	$688.92		$755.8293	$755.82	$755.80	$755.80