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	$63.43	6.240%	$67.388	$67.39	$67.40	$67.40
Purchase #2	$112.39	8.713%	$122.1825	$122.18	$122.20	$122.20
Purchase #3	$83.82	8.266%	$90.7486	$90.75	$90.75	$90.70
Purchase #4	$108.74	5.241%	$114.4391	$114.44	$114.45	$114.40
Purchase #5	$92.31	7.405%	$99.1456	$99.15	$99.15	$99.10
Purchase #6	$152.82	11.513%	$170.4142	$170.41	$170.40	$170.40
Purchase #7	$232.73	4.230%	$242.5745	$242.57	$242.55	$242.60
7 purchase totals =	$846.24		$906.8925	$906.89	$906.90	$906.80