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	$174.48	8.197%	$188.7821	$188.78	$188.80	$188.80
Purchase #2	$129.93	7.451%	$139.6111	$139.61	$139.60	$139.60
Purchase #3	$173.48	5.480%	$182.9867	$182.99	$183.00	$183.00
Purchase #4	$170.56	13.117%	$192.9324	$192.93	$192.95	$192.90
Purchase #5	$89.64	12.612%	$100.9454	$100.95	$100.95	$100.90
Purchase #6	$245.78	13.512%	$278.9898	$278.99	$279.00	$279.00
Purchase #7	$228.73	11.745%	$255.5943	$255.59	$255.60	$255.60
7 purchase totals =	$1,212.60		$1,339.8418	$1,339.84	$1,339.90	$1,339.80