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	$104.30	4.587%	$109.0842	$109.08	$109.10	$109.10
Purchase #2	$233.34	13.512%	$264.8689	$264.87	$264.85	$264.90
Purchase #3	$108.69	7.378%	$116.7091	$116.71	$116.70	$116.70
Purchase #4	$94.52	8.552%	$102.6034	$102.60	$102.60	$102.60
Purchase #5	$106.71	11.131%	$118.5879	$118.59	$118.60	$118.60
Purchase #6	$172.30	4.687%	$180.3757	$180.38	$180.40	$180.40
Purchase #7	$77.99	4.510%	$81.5073	$81.51	$81.50	$81.50
7 purchase totals =	$897.85		$973.7365	$973.74	$973.75	$973.80