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	$86.83	4.343%	$90.601	$90.60	$90.60	$90.60
Purchase #2	$94.30	10.497%	$104.1987	$104.20	$104.20	$104.20
Purchase #3	$149.31	6.473%	$158.9748	$158.97	$158.95	$159.00
Purchase #4	$222.81	10.432%	$246.0535	$246.05	$246.05	$246.10
Purchase #5	$153.31	12.721%	$172.8126	$172.81	$172.80	$172.80
Purchase #6	$11.54	13.841%	$13.1373	$13.14	$13.15	$13.10
Purchase #7	$37.72	10.870%	$41.8202	$41.82	$41.80	$41.80
7 purchase totals =	$755.82		$827.5981	$827.59	$827.55	$827.60