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	$41.46	3.574%	$42.9418	$42.94	$42.95	$42.90
Purchase #2	$17.41	10.534%	$19.244	$19.24	$19.25	$19.20
Purchase #3	$33.78	7.789%	$36.4111	$36.41	$36.40	$36.40
Purchase #4	$65.37	4.810%	$68.5143	$68.51	$68.50	$68.50
Purchase #5	$128.59	8.801%	$139.9072	$139.91	$139.90	$139.90
Purchase #6	$237.41	12.853%	$267.9243	$267.92	$267.90	$267.90
Purchase #7	$60.40	10.388%	$66.6744	$66.67	$66.65	$66.70
7 purchase totals =	$584.42		$641.6171	$641.60	$641.55	$641.50