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	$240.49	3.539%	$249.0009	$249.00	$249.00	$249.00
Purchase #2	$180.85	12.716%	$203.8469	$203.85	$203.85	$203.80
Purchase #3	$62.71	5.246%	$65.9998	$66.00	$66.00	$66.00
Purchase #4	$143.61	5.506%	$151.5172	$151.52	$151.50	$151.50
Purchase #5	$238.73	4.530%	$249.5445	$249.54	$249.55	$249.50
Purchase #6	$198.47	3.610%	$205.6348	$205.63	$205.65	$205.60
Purchase #7	$47.52	13.136%	$53.7622	$53.76	$53.75	$53.80
7 purchase totals =	$1,112.38		$1,179.3063	$1,179.30	$1,179.30	$1,179.20