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	$79.81	11.234%	$88.7759	$88.78	$88.80	$88.80
Purchase #2	$9.89	8.560%	$10.7366	$10.74	$10.75	$10.70
Purchase #3	$39.89	13.614%	$45.3206	$45.32	$45.30	$45.30
Purchase #4	$144.72	5.855%	$153.1934	$153.19	$153.20	$153.20
Purchase #5	$33.68	9.445%	$36.8611	$36.86	$36.85	$36.90
Purchase #6	$143.96	7.344%	$154.5324	$154.53	$154.55	$154.50
Purchase #7	$139.60	7.642%	$150.2682	$150.27	$150.25	$150.30
7 purchase totals =	$591.55		$639.6882	$639.69	$639.70	$639.70