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	$180.44	6.736%	$192.5944	$192.59	$192.60	$192.60
Purchase #2	$116.93	12.678%	$131.7544	$131.75	$131.75	$131.80
Purchase #3	$222.93	10.832%	$247.0778	$247.08	$247.10	$247.10
Purchase #4	$87.76	12.454%	$98.6896	$98.69	$98.70	$98.70
Purchase #5	$103.97	8.188%	$112.4831	$112.48	$112.50	$112.50
Purchase #6	$63.61	4.267%	$66.3242	$66.32	$66.30	$66.30
Purchase #7	$82.88	9.180%	$90.4884	$90.49	$90.50	$90.50
7 purchase totals =	$858.52		$939.4119	$939.40	$939.45	$939.50