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	$136.65	7.203%	$146.4929	$146.49	$146.50	$146.50
Purchase #2	$233.39	8.768%	$253.8536	$253.85	$253.85	$253.90
Purchase #3	$164.67	12.304%	$184.931	$184.93	$184.95	$184.90
Purchase #4	$228.45	4.527%	$238.7919	$238.79	$238.80	$238.80
Purchase #5	$73.92	11.256%	$82.2404	$82.24	$82.25	$82.20
Purchase #6	$204.99	5.338%	$215.9324	$215.93	$215.95	$215.90
Purchase #7	$152.26	12.712%	$171.6153	$171.62	$171.60	$171.60
7 purchase totals =	$1,194.33		$1,293.8575	$1,293.85	$1,293.90	$1,293.80