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	$57.89	5.674%	$61.1747	$61.17	$61.15	$61.20
Purchase #2	$162.33	6.801%	$173.3701	$173.37	$173.35	$173.40
Purchase #3	$200.59	11.855%	$224.3699	$224.37	$224.35	$224.40
Purchase #4	$57.99	12.301%	$65.1233	$65.12	$65.10	$65.10
Purchase #5	$165.67	3.461%	$171.4038	$171.40	$171.40	$171.40
Purchase #6	$34.46	13.278%	$39.0356	$39.04	$39.05	$39.00
Purchase #7	$173.74	6.763%	$185.49	$185.49	$185.50	$185.50
7 purchase totals =	$852.67		$919.9674	$919.96	$919.90	$920.00