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	$81.56	11.343%	$90.8114	$90.81	$90.80	$90.80
Purchase #2	$10.99	3.546%	$11.3797	$11.38	$11.40	$11.40
Purchase #3	$166.42	5.618%	$175.7695	$175.77	$175.75	$175.80
Purchase #4	$79.71	4.566%	$83.3496	$83.35	$83.35	$83.30
Purchase #5	$99.80	11.549%	$111.3259	$111.33	$111.35	$111.30
Purchase #6	$21.42	3.461%	$22.1613	$22.16	$22.15	$22.20
Purchase #7	$110.82	11.483%	$123.5455	$123.55	$123.55	$123.50
7 purchase totals =	$570.72		$618.3429	$618.35	$618.35	$618.30