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	$229.63	11.420%	$255.8537	$255.85	$255.85	$255.90
Purchase #2	$85.99	4.842%	$90.1536	$90.15	$90.15	$90.20
Purchase #3	$54.97	7.443%	$59.0614	$59.06	$59.05	$59.10
Purchase #4	$113.60	9.831%	$124.768	$124.77	$124.75	$124.80
Purchase #5	$14.33	13.823%	$16.3108	$16.31	$16.30	$16.30
Purchase #6	$145.41	8.226%	$157.3714	$157.37	$157.35	$157.40
Purchase #7	$87.35	12.362%	$98.1482	$98.15	$98.15	$98.10
7 purchase totals =	$731.28		$801.6671	$801.66	$801.60	$801.80