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	$240.77	6.704%	$256.9112	$256.91	$256.90	$256.90
Purchase #2	$37.28	13.725%	$42.3967	$42.40	$42.40	$42.40
Purchase #3	$191.42	13.602%	$217.4569	$217.46	$217.45	$217.50
Purchase #4	$166.56	10.346%	$183.7923	$183.79	$183.80	$183.80
Purchase #5	$22.53	11.394%	$25.0971	$25.10	$25.10	$25.10
Purchase #6	$162.78	5.287%	$171.3862	$171.39	$171.40	$171.40
Purchase #7	$223.52	11.191%	$248.5341	$248.53	$248.55	$248.50
7 purchase totals =	$1,044.86		$1,145.5745	$1,145.58	$1,145.60	$1,145.60