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	$29.50	10.411%	$32.5712	$32.57	$32.55	$32.60
Purchase #2	$161.79	11.204%	$179.917	$179.92	$179.90	$179.90
Purchase #3	$74.91	6.183%	$79.5417	$79.54	$79.55	$79.50
Purchase #4	$38.60	6.816%	$41.231	$41.23	$41.25	$41.20
Purchase #5	$52.86	12.171%	$59.2936	$59.29	$59.30	$59.30
Purchase #6	$166.31	13.423%	$188.6338	$188.63	$188.65	$188.60
Purchase #7	$157.26	9.672%	$172.4702	$172.47	$172.45	$172.50
7 purchase totals =	$681.23		$753.6585	$753.65	$753.65	$753.60