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	$28.78	13.227%	$32.5867	$32.59	$32.60	$32.60
Purchase #2	$249.41	6.611%	$265.8985	$265.90	$265.90	$265.90
Purchase #3	$40.45	10.497%	$44.696	$44.70	$44.70	$44.70
Purchase #4	$75.34	10.475%	$83.2319	$83.23	$83.25	$83.20
Purchase #5	$136.27	7.489%	$146.4753	$146.48	$146.50	$146.50
Purchase #6	$53.82	12.414%	$60.5012	$60.50	$60.50	$60.50
Purchase #7	$48.91	11.713%	$54.6388	$54.64	$54.65	$54.60
7 purchase totals =	$632.98		$688.0284	$688.04	$688.10	$688.00