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	$150.98	5.653%	$159.5149	$159.51	$159.50	$159.50
Purchase #2	$213.70	4.557%	$223.4383	$223.44	$223.45	$223.40
Purchase #3	$232.87	9.603%	$255.2325	$255.23	$255.25	$255.20
Purchase #4	$30.95	6.719%	$33.0295	$33.03	$33.05	$33.00
Purchase #5	$53.33	7.810%	$57.4951	$57.50	$57.50	$57.50
Purchase #6	$145.44	5.694%	$153.7214	$153.72	$153.70	$153.70
Purchase #7	$220.63	9.858%	$242.3797	$242.38	$242.40	$242.40
7 purchase totals =	$1,047.90		$1,124.8114	$1,124.81	$1,124.85	$1,124.70