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	$155.61	10.861%	$172.5108	$172.51	$172.50	$172.50
Purchase #2	$51.41	12.604%	$57.8897	$57.89	$57.90	$57.90
Purchase #3	$62.99	4.276%	$65.6835	$65.68	$65.70	$65.70
Purchase #4	$28.29	5.485%	$29.8417	$29.84	$29.85	$29.80
Purchase #5	$102.62	3.822%	$106.5421	$106.54	$106.55	$106.50
Purchase #6	$77.49	10.137%	$85.3452	$85.35	$85.35	$85.30
Purchase #7	$79.88	6.714%	$85.2431	$85.24	$85.25	$85.20
7 purchase totals =	$558.29		$603.0561	$603.05	$603.10	$602.90