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	$215.91	4.594%	$225.8289	$225.83	$225.85	$225.80
Purchase #2	$135.94	7.117%	$145.6148	$145.61	$145.60	$145.60
Purchase #3	$100.37	11.299%	$111.7108	$111.71	$111.70	$111.70
Purchase #4	$89.71	9.820%	$98.5195	$98.52	$98.50	$98.50
Purchase #5	$230.28	8.510%	$249.8768	$249.88	$249.90	$249.90
Purchase #6	$124.85	12.511%	$140.47	$140.47	$140.45	$140.50
Purchase #7	$242.56	10.852%	$268.8826	$268.88	$268.90	$268.90
7 purchase totals =	$1,139.62		$1,240.9034	$1,240.90	$1,240.90	$1,240.90