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	$74.42	13.726%	$84.6349	$84.63	$84.65	$84.60
Purchase #2	$205.95	10.838%	$228.2709	$228.27	$228.25	$228.30
Purchase #3	$223.87	6.420%	$238.2425	$238.24	$238.25	$238.20
Purchase #4	$24.51	11.215%	$27.2588	$27.26	$27.25	$27.30
Purchase #5	$98.64	3.287%	$101.8823	$101.88	$101.90	$101.90
Purchase #6	$244.46	11.794%	$273.2916	$273.29	$273.30	$273.30
Purchase #7	$90.75	11.155%	$100.8732	$100.87	$100.85	$100.90
7 purchase totals =	$962.60		$1,054.4542	$1,054.44	$1,054.45	$1,054.50