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	$77.38	10.497%	$85.5026	$85.50	$85.50	$85.50
Purchase #2	$130.32	12.191%	$146.2073	$146.21	$146.20	$146.20
Purchase #3	$148.73	11.623%	$166.0169	$166.02	$166.00	$166.00
Purchase #4	$122.43	4.467%	$127.8989	$127.90	$127.90	$127.90
Purchase #5	$80.81	13.263%	$91.5278	$91.53	$91.55	$91.50
Purchase #6	$162.85	8.117%	$176.0685	$176.07	$176.05	$176.10
Purchase #7	$192.63	12.333%	$216.3871	$216.39	$216.40	$216.40
7 purchase totals =	$915.15		$1,009.6091	$1,009.62	$1,009.60	$1,009.60