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	$52.68	4.643%	$55.1259	$55.13	$55.15	$55.10
Purchase #2	$147.94	13.131%	$167.366	$167.37	$167.35	$167.40
Purchase #3	$91.52	6.261%	$97.2501	$97.25	$97.25	$97.30
Purchase #4	$71.79	9.321%	$78.4815	$78.48	$78.50	$78.50
Purchase #5	$224.42	7.777%	$241.8731	$241.87	$241.85	$241.90
Purchase #6	$104.48	13.697%	$118.7906	$118.79	$118.80	$118.80
Purchase #7	$68.49	12.586%	$77.1102	$77.11	$77.10	$77.10
7 purchase totals =	$761.32		$835.9974	$836.00	$836.00	$836.10