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	$192.76	12.500%	$216.855	$216.86	$216.85	$216.90
Purchase #2	$230.91	5.421%	$243.4276	$243.43	$243.45	$243.40
Purchase #3	$80.25	12.371%	$90.1777	$90.18	$90.20	$90.20
Purchase #4	$41.70	4.857%	$43.7254	$43.73	$43.75	$43.70
Purchase #5	$88.42	3.828%	$91.8047	$91.80	$91.80	$91.80
Purchase #6	$92.99	11.764%	$103.9293	$103.93	$103.95	$103.90
Purchase #7	$131.63	12.677%	$148.3167	$148.32	$148.30	$148.30
7 purchase totals =	$858.66		$938.2364	$938.25	$938.30	$938.20