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	$52.88	5.715%	$55.9021	$55.90	$55.90	$55.90
Purchase #2	$188.63	6.377%	$200.6589	$200.66	$200.65	$200.70
Purchase #3	$175.47	3.606%	$181.7974	$181.80	$181.80	$181.80
Purchase #4	$236.85	4.657%	$247.8801	$247.88	$247.90	$247.90
Purchase #5	$29.49	13.832%	$33.5691	$33.57	$33.55	$33.60
Purchase #6	$188.78	7.844%	$203.5879	$203.59	$203.60	$203.60
Purchase #7	$244.61	12.661%	$275.5801	$275.58	$275.60	$275.60
7 purchase totals =	$1,116.71		$1,198.9756	$1,198.98	$1,199.00	$1,199.10