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	$52.62	4.279%	$54.8716	$54.87	$54.85	$54.90
Purchase #2	$21.94	13.410%	$24.8822	$24.88	$24.90	$24.90
Purchase #3	$7.74	13.170%	$8.7594	$8.76	$8.75	$8.80
Purchase #4	$37.52	12.736%	$42.2985	$42.30	$42.30	$42.30
Purchase #5	$165.65	7.399%	$177.9064	$177.91	$177.90	$177.90
Purchase #6	$247.79	13.103%	$280.2579	$280.26	$280.25	$280.30
Purchase #7	$72.55	5.361%	$76.4394	$76.44	$76.45	$76.40
7 purchase totals =	$605.81		$665.4154	$665.42	$665.40	$665.50