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	$80.52	11.156%	$89.5028	$89.50	$89.50	$89.50
Purchase #2	$100.94	11.460%	$112.5077	$112.51	$112.50	$112.50
Purchase #3	$28.66	4.455%	$29.9368	$29.94	$29.95	$29.90
Purchase #4	$51.56	13.484%	$58.5124	$58.51	$58.50	$58.50
Purchase #5	$130.99	3.626%	$135.7397	$135.74	$135.75	$135.70
Purchase #6	$37.91	10.156%	$41.7601	$41.76	$41.75	$41.80
Purchase #7	$90.77	10.505%	$100.3054	$100.31	$100.30	$100.30
7 purchase totals =	$521.35		$568.2649	$568.27	$568.25	$568.20