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	$52.83	9.614%	$57.9091	$57.91	$57.90	$57.90
Purchase #2	$230.79	6.189%	$245.0736	$245.07	$245.05	$245.10
Purchase #3	$119.91	7.830%	$129.299	$129.30	$129.30	$129.30
Purchase #4	$188.34	4.298%	$196.4349	$196.43	$196.45	$196.40
Purchase #5	$64.68	12.715%	$72.9041	$72.90	$72.90	$72.90
Purchase #6	$132.71	10.302%	$146.3818	$146.38	$146.40	$146.40
Purchase #7	$105.53	4.105%	$109.862	$109.86	$109.85	$109.90
7 purchase totals =	$894.79		$957.8645	$957.85	$957.85	$957.90