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	$47.45	4.305%	$49.4927	$49.49	$49.50	$49.50
Purchase #2	$223.53	4.487%	$233.5598	$233.56	$233.55	$233.60
Purchase #3	$16.44	13.852%	$18.7173	$18.72	$18.70	$18.70
Purchase #4	$245.90	10.588%	$271.9359	$271.94	$271.95	$271.90
Purchase #5	$55.62	8.590%	$60.3978	$60.40	$60.40	$60.40
Purchase #6	$141.28	10.820%	$156.5665	$156.57	$156.55	$156.60
Purchase #7	$93.90	6.246%	$99.765	$99.77	$99.75	$99.80
7 purchase totals =	$824.12		$890.4350	$890.45	$890.40	$890.50