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	$68.76	13.144%	$77.7978	$77.80	$77.80	$77.80
Purchase #2	$27.91	7.103%	$29.8924	$29.89	$29.90	$29.90
Purchase #3	$93.28	7.325%	$100.1128	$100.11	$100.10	$100.10
Purchase #4	$58.32	8.223%	$63.1157	$63.12	$63.10	$63.10
Purchase #5	$37.66	3.559%	$39.0003	$39.00	$39.00	$39.00
Purchase #6	$171.89	6.192%	$182.5334	$182.53	$182.55	$182.50
Purchase #7	$95.81	3.677%	$99.3329	$99.33	$99.35	$99.30
7 purchase totals =	$553.63		$591.7853	$591.78	$591.80	$591.70