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	$14.86	4.278%	$15.4957	$15.50	$15.50	$15.50
Purchase #2	$238.38	10.603%	$263.6554	$263.66	$263.65	$263.70
Purchase #3	$42.99	11.233%	$47.8191	$47.82	$47.80	$47.80
Purchase #4	$41.69	10.512%	$46.0725	$46.07	$46.05	$46.10
Purchase #5	$181.71	9.306%	$198.6199	$198.62	$198.60	$198.60
Purchase #6	$64.53	12.380%	$72.5188	$72.52	$72.50	$72.50
Purchase #7	$83.67	8.172%	$90.5075	$90.51	$90.50	$90.50
7 purchase totals =	$667.83		$734.6889	$734.70	$734.60	$734.70