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	$97.64	12.117%	$109.471	$109.47	$109.45	$109.50
Purchase #2	$213.77	10.739%	$236.7268	$236.73	$236.75	$236.70
Purchase #3	$6.59	13.346%	$7.4695	$7.47	$7.45	$7.50
Purchase #4	$208.47	11.154%	$231.7227	$231.72	$231.70	$231.70
Purchase #5	$96.32	4.706%	$100.8528	$100.85	$100.85	$100.90
Purchase #6	$92.45	11.386%	$102.9764	$102.98	$103.00	$103.00
Purchase #7	$101.63	5.380%	$107.0977	$107.10	$107.10	$107.10
7 purchase totals =	$816.87		$896.3169	$896.32	$896.30	$896.40