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	$107.52	4.594%	$112.4595	$112.46	$112.45	$112.50
Purchase #2	$89.81	11.371%	$100.0223	$100.02	$100.00	$100.00
Purchase #3	$141.87	6.271%	$150.7667	$150.77	$150.75	$150.80
Purchase #4	$130.68	9.298%	$142.8306	$142.83	$142.85	$142.80
Purchase #5	$38.99	8.549%	$42.3233	$42.32	$42.30	$42.30
Purchase #6	$138.65	7.152%	$148.5662	$148.57	$148.55	$148.60
Purchase #7	$243.74	6.669%	$259.995	$260.00	$260.00	$260.00
7 purchase totals =	$891.26		$956.9636	$956.97	$956.90	$957.00