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	$126.68	7.533%	$136.2228	$136.22	$136.20	$136.20
Purchase #2	$245.92	12.158%	$275.819	$275.82	$275.80	$275.80
Purchase #3	$111.75	11.139%	$124.1978	$124.20	$124.20	$124.20
Purchase #4	$115.50	5.528%	$121.8848	$121.88	$121.90	$121.90
Purchase #5	$151.58	9.615%	$166.1544	$166.15	$166.15	$166.20
Purchase #6	$168.74	5.638%	$178.2536	$178.25	$178.25	$178.30
Purchase #7	$96.71	6.842%	$103.3269	$103.33	$103.35	$103.30
7 purchase totals =	$1,016.88		$1,105.8593	$1,105.85	$1,105.85	$1,105.90