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	$112.34	10.657%	$124.3121	$124.31	$124.30	$124.30
Purchase #2	$165.73	8.126%	$179.1972	$179.20	$179.20	$179.20
Purchase #3	$217.38	3.664%	$225.3448	$225.34	$225.35	$225.30
Purchase #4	$171.56	7.395%	$184.2469	$184.25	$184.25	$184.20
Purchase #5	$62.60	6.846%	$66.8856	$66.89	$66.90	$66.90
Purchase #6	$40.89	6.395%	$43.5049	$43.50	$43.50	$43.50
Purchase #7	$60.63	4.103%	$63.1176	$63.12	$63.10	$63.10
7 purchase totals =	$831.13		$886.6091	$886.61	$886.60	$886.50