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	$7.67	3.188%	$7.9145	$7.91	$7.90	$7.90
Purchase #2	$96.26	5.738%	$101.7834	$101.78	$101.80	$101.80
Purchase #3	$60.42	6.232%	$64.1854	$64.19	$64.20	$64.20
Purchase #4	$244.41	4.309%	$254.9416	$254.94	$254.95	$254.90
Purchase #5	$99.56	5.611%	$105.1463	$105.15	$105.15	$105.10
Purchase #6	$129.53	11.563%	$144.5076	$144.51	$144.50	$144.50
Purchase #7	$56.49	4.707%	$59.149	$59.15	$59.15	$59.10
7 purchase totals =	$694.34		$737.6278	$737.63	$737.65	$737.50