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	$35.50	13.164%	$40.1732	$40.17	$40.15	$40.20
Purchase #2	$149.83	7.425%	$160.9549	$160.95	$160.95	$161.00
Purchase #3	$47.75	12.680%	$53.8047	$53.80	$53.80	$53.80
Purchase #4	$55.39	10.195%	$61.037	$61.04	$61.05	$61.00
Purchase #5	$170.76	7.759%	$184.0093	$184.01	$184.00	$184.00
Purchase #6	$233.61	8.450%	$253.35	$253.35	$253.35	$253.40
Purchase #7	$61.89	6.426%	$65.8671	$65.87	$65.85	$65.90
7 purchase totals =	$754.73		$819.1962	$819.19	$819.15	$819.30