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	$72.57	7.650%	$78.1216	$78.12	$78.10	$78.10
Purchase #2	$187.50	10.810%	$207.7688	$207.77	$207.75	$207.80
Purchase #3	$20.32	9.605%	$22.2717	$22.27	$22.25	$22.30
Purchase #4	$108.57	13.680%	$123.4224	$123.42	$123.40	$123.40
Purchase #5	$158.91	9.619%	$174.1956	$174.20	$174.20	$174.20
Purchase #6	$136.66	11.508%	$152.3868	$152.39	$152.40	$152.40
Purchase #7	$196.71	12.376%	$221.0548	$221.05	$221.05	$221.10
7 purchase totals =	$881.24		$979.2217	$979.22	$979.15	$979.30