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	$108.75	13.235%	$123.1431	$123.14	$123.15	$123.10
Purchase #2	$83.66	5.607%	$88.3508	$88.35	$88.35	$88.40
Purchase #3	$225.93	5.411%	$238.1551	$238.16	$238.15	$238.20
Purchase #4	$165.25	4.212%	$172.2103	$172.21	$172.20	$172.20
Purchase #5	$64.90	10.753%	$71.8787	$71.88	$71.90	$71.90
Purchase #6	$91.91	11.684%	$102.6488	$102.65	$102.65	$102.60
Purchase #7	$51.42	5.164%	$54.0753	$54.08	$54.10	$54.10
7 purchase totals =	$791.82		$850.4621	$850.47	$850.50	$850.50