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	$102.35	3.340%	$105.7685	$105.77	$105.75	$105.80
Purchase #2	$227.26	12.329%	$255.2789	$255.28	$255.30	$255.30
Purchase #3	$106.83	6.692%	$113.9791	$113.98	$114.00	$114.00
Purchase #4	$101.41	9.169%	$110.7083	$110.71	$110.70	$110.70
Purchase #5	$113.83	12.822%	$128.4253	$128.43	$128.45	$128.40
Purchase #6	$135.80	10.871%	$150.5628	$150.56	$150.55	$150.60
Purchase #7	$92.68	7.821%	$99.9285	$99.93	$99.95	$99.90
7 purchase totals =	$880.16		$964.6514	$964.66	$964.70	$964.70