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	$65.48	6.846%	$69.9628	$69.96	$69.95	$70.00
Purchase #2	$82.63	12.295%	$92.7894	$92.79	$92.80	$92.80
Purchase #3	$62.73	4.808%	$65.7461	$65.75	$65.75	$65.70
Purchase #4	$152.51	9.260%	$166.6324	$166.63	$166.65	$166.60
Purchase #5	$95.74	5.326%	$100.8391	$100.84	$100.85	$100.80
Purchase #6	$166.63	3.623%	$172.667	$172.67	$172.65	$172.70
Purchase #7	$157.31	6.486%	$167.5131	$167.51	$167.50	$167.50
7 purchase totals =	$783.03		$836.1499	$836.15	$836.15	$836.10