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	$160.38	12.266%	$180.0522	$180.05	$180.05	$180.10
Purchase #2	$99.78	11.648%	$111.4024	$111.40	$111.40	$111.40
Purchase #3	$82.35	9.621%	$90.2729	$90.27	$90.25	$90.30
Purchase #4	$218.38	13.430%	$247.7084	$247.71	$247.70	$247.70
Purchase #5	$210.59	3.857%	$218.7125	$218.71	$218.70	$218.70
Purchase #6	$77.98	3.337%	$80.5822	$80.58	$80.60	$80.60
Purchase #7	$33.59	7.573%	$36.1338	$36.13	$36.15	$36.10
7 purchase totals =	$883.05		$964.8644	$964.85	$964.85	$964.90