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	$90.42	10.278%	$99.7134	$99.71	$99.70	$99.70
Purchase #2	$238.83	13.352%	$270.7186	$270.72	$270.70	$270.70
Purchase #3	$166.82	7.640%	$179.565	$179.57	$179.55	$179.60
Purchase #4	$99.53	4.360%	$103.8695	$103.87	$103.85	$103.90
Purchase #5	$116.73	10.497%	$128.9831	$128.98	$129.00	$129.00
Purchase #6	$97.62	10.813%	$108.1757	$108.18	$108.20	$108.20
Purchase #7	$157.55	12.257%	$176.8609	$176.86	$176.85	$176.90
7 purchase totals =	$967.50		$1,067.8862	$1,067.89	$1,067.85	$1,068.00