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	$25.80	13.631%	$29.3168	$29.32	$29.30	$29.30
Purchase #2	$225.49	11.244%	$250.8441	$250.84	$250.85	$250.80
Purchase #3	$159.34	8.285%	$172.5413	$172.54	$172.55	$172.50
Purchase #4	$190.66	3.587%	$197.499	$197.50	$197.50	$197.50
Purchase #5	$50.75	7.874%	$54.7461	$54.75	$54.75	$54.70
Purchase #6	$158.78	11.753%	$177.4414	$177.44	$177.45	$177.40
Purchase #7	$119.66	12.340%	$134.426	$134.43	$134.45	$134.40
7 purchase totals =	$930.48		$1,016.8147	$1,016.82	$1,016.85	$1,016.60