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	$35.61	13.654%	$40.4722	$40.47	$40.45	$40.50
Purchase #2	$86.81	10.427%	$95.8617	$95.86	$95.85	$95.90
Purchase #3	$158.26	12.772%	$178.473	$178.47	$178.45	$178.50
Purchase #4	$130.50	8.820%	$142.0101	$142.01	$142.00	$142.00
Purchase #5	$80.51	4.388%	$84.0428	$84.04	$84.05	$84.00
Purchase #6	$15.95	9.379%	$17.446	$17.45	$17.45	$17.40
Purchase #7	$38.30	11.797%	$42.8183	$42.82	$42.80	$42.80
7 purchase totals =	$545.94		$601.1241	$601.12	$601.05	$601.10