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	$249.83	3.323%	$258.1319	$258.13	$258.15	$258.10
Purchase #2	$157.86	9.331%	$172.5899	$172.59	$172.60	$172.60
Purchase #3	$13.83	13.823%	$15.7417	$15.74	$15.75	$15.70
Purchase #4	$140.98	5.588%	$148.858	$148.86	$148.85	$148.90
Purchase #5	$216.63	13.170%	$245.1602	$245.16	$245.15	$245.20
Purchase #6	$205.53	10.841%	$227.8115	$227.81	$227.80	$227.80
Purchase #7	$45.32	13.185%	$51.2954	$51.30	$51.30	$51.30
7 purchase totals =	$1,029.98		$1,119.5886	$1,119.59	$1,119.60	$1,119.60