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	$6.67	7.308%	$7.1574	$7.16	$7.15	$7.20
Purchase #2	$148.86	10.322%	$164.2253	$164.23	$164.25	$164.20
Purchase #3	$152.43	10.720%	$168.7705	$168.77	$168.75	$168.80
Purchase #4	$10.78	3.453%	$11.1522	$11.15	$11.15	$11.20
Purchase #5	$135.55	9.187%	$148.003	$148.00	$148.00	$148.00
Purchase #6	$93.83	12.146%	$105.2266	$105.23	$105.25	$105.20
Purchase #7	$190.74	10.454%	$210.68	$210.68	$210.70	$210.70
7 purchase totals =	$738.86		$815.2150	$815.22	$815.25	$815.30