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	$51.90	6.543%	$55.2958	$55.30	$55.30	$55.30
Purchase #2	$105.69	4.667%	$110.6226	$110.62	$110.60	$110.60
Purchase #3	$239.33	11.487%	$266.8218	$266.82	$266.80	$266.80
Purchase #4	$197.85	9.798%	$217.2353	$217.24	$217.25	$217.20
Purchase #5	$218.97	11.104%	$243.2844	$243.28	$243.30	$243.30
Purchase #6	$97.66	3.195%	$100.7802	$100.78	$100.80	$100.80
Purchase #7	$35.94	12.707%	$40.5069	$40.51	$40.50	$40.50
7 purchase totals =	$947.34		$1,034.5470	$1,034.55	$1,034.55	$1,034.50