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	$60.42	6.578%	$64.3944	$64.39	$64.40	$64.40
Purchase #2	$73.85	13.445%	$83.7791	$83.78	$83.80	$83.80
Purchase #3	$203.72	10.523%	$225.1575	$225.16	$225.15	$225.20
Purchase #4	$75.43	10.851%	$83.6149	$83.61	$83.60	$83.60
Purchase #5	$118.34	9.197%	$129.2237	$129.22	$129.20	$129.20
Purchase #6	$93.49	9.546%	$102.4146	$102.41	$102.40	$102.40
Purchase #7	$93.72	7.501%	$100.7499	$100.75	$100.75	$100.70
7 purchase totals =	$718.97		$789.3341	$789.32	$789.30	$789.30