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	$25.53	6.277%	$27.1325	$27.13	$27.15	$27.10
Purchase #2	$175.62	11.340%	$195.5353	$195.54	$195.55	$195.50
Purchase #3	$183.76	6.719%	$196.1068	$196.11	$196.10	$196.10
Purchase #4	$180.89	3.531%	$187.2772	$187.28	$187.30	$187.30
Purchase #5	$47.88	8.143%	$51.7789	$51.78	$51.80	$51.80
Purchase #6	$235.47	13.166%	$266.472	$266.47	$266.45	$266.50
Purchase #7	$87.42	5.611%	$92.3251	$92.33	$92.35	$92.30
7 purchase totals =	$936.57		$1,016.6278	$1,016.64	$1,016.70	$1,016.60