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	$248.36	11.120%	$275.9776	$275.98	$276.00	$276.00
Purchase #2	$156.83	8.831%	$170.6797	$170.68	$170.70	$170.70
Purchase #3	$111.28	10.838%	$123.3405	$123.34	$123.35	$123.30
Purchase #4	$155.36	7.448%	$166.9312	$166.93	$166.95	$166.90
Purchase #5	$94.39	6.823%	$100.8302	$100.83	$100.85	$100.80
Purchase #6	$133.33	3.347%	$137.7926	$137.79	$137.80	$137.80
Purchase #7	$170.53	5.638%	$180.1445	$180.14	$180.15	$180.10
7 purchase totals =	$1,070.08		$1,155.6963	$1,155.69	$1,155.80	$1,155.60