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	$103.40	8.231%	$111.9109	$111.91	$111.90	$111.90
Purchase #2	$171.69	11.184%	$190.8918	$190.89	$190.90	$190.90
Purchase #3	$37.45	12.736%	$42.2196	$42.22	$42.20	$42.20
Purchase #4	$175.73	6.398%	$186.9732	$186.97	$186.95	$187.00
Purchase #5	$67.68	10.422%	$74.7336	$74.73	$74.75	$74.70
Purchase #6	$177.78	3.392%	$183.8103	$183.81	$183.80	$183.80
Purchase #7	$116.47	11.200%	$129.5146	$129.51	$129.50	$129.50
7 purchase totals =	$850.20		$920.0540	$920.04	$920.00	$920.00