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	$9.59	4.451%	$10.0169	$10.02	$10.00	$10.00
Purchase #2	$38.44	4.363%	$40.1171	$40.12	$40.10	$40.10
Purchase #3	$61.76	6.810%	$65.9659	$65.97	$65.95	$66.00
Purchase #4	$234.69	8.841%	$255.4389	$255.44	$255.45	$255.40
Purchase #5	$242.74	5.120%	$255.1683	$255.17	$255.15	$255.20
Purchase #6	$192.61	4.759%	$201.7763	$201.78	$201.80	$201.80
Purchase #7	$183.65	9.114%	$200.3879	$200.39	$200.40	$200.40
7 purchase totals =	$963.48		$1,028.8713	$1,028.89	$1,028.85	$1,028.90