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	$72.74	3.771%	$75.483	$75.48	$75.50	$75.50
Purchase #2	$39.55	5.136%	$41.5813	$41.58	$41.60	$41.60
Purchase #3	$89.46	10.720%	$99.0501	$99.05	$99.05	$99.10
Purchase #4	$87.53	6.773%	$93.4584	$93.46	$93.45	$93.50
Purchase #5	$165.89	4.229%	$172.9055	$172.91	$172.90	$172.90
Purchase #6	$126.38	12.184%	$141.7781	$141.78	$141.80	$141.80
Purchase #7	$38.65	11.155%	$42.9614	$42.96	$42.95	$43.00
7 purchase totals =	$620.20		$667.2178	$667.22	$667.25	$667.40