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	$249.61	11.482%	$278.2702	$278.27	$278.25	$278.30
Purchase #2	$76.83	7.332%	$82.4632	$82.46	$82.45	$82.50
Purchase #3	$109.25	13.671%	$124.1856	$124.19	$124.20	$124.20
Purchase #4	$169.58	12.204%	$190.2755	$190.28	$190.30	$190.30
Purchase #5	$39.64	12.345%	$44.5336	$44.53	$44.55	$44.50
Purchase #6	$41.64	5.293%	$43.844	$43.84	$43.85	$43.80
Purchase #7	$48.99	9.407%	$53.5985	$53.60	$53.60	$53.60
7 purchase totals =	$735.54		$817.1706	$817.17	$817.20	$817.20