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	$31.98	4.739%	$33.4955	$33.50	$33.50	$33.50
Purchase #2	$151.87	4.610%	$158.8712	$158.87	$158.85	$158.90
Purchase #3	$195.32	12.802%	$220.3249	$220.32	$220.30	$220.30
Purchase #4	$220.77	5.716%	$233.3892	$233.39	$233.40	$233.40
Purchase #5	$34.31	6.261%	$36.4581	$36.46	$36.45	$36.50
Purchase #6	$105.92	5.788%	$112.0506	$112.05	$112.05	$112.10
Purchase #7	$122.80	6.859%	$131.2229	$131.22	$131.20	$131.20
7 purchase totals =	$862.97		$925.8124	$925.81	$925.75	$925.90