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	$29.33	12.513%	$33.0001	$33.00	$33.00	$33.00
Purchase #2	$175.96	9.338%	$192.3911	$192.39	$192.40	$192.40
Purchase #3	$65.51	9.681%	$71.852	$71.85	$71.85	$71.90
Purchase #4	$220.86	6.374%	$234.9376	$234.94	$234.95	$234.90
Purchase #5	$204.46	13.205%	$231.4589	$231.46	$231.45	$231.50
Purchase #6	$48.98	4.772%	$51.3173	$51.32	$51.30	$51.30
Purchase #7	$165.60	13.848%	$188.5323	$188.53	$188.55	$188.50
7 purchase totals =	$910.70		$1,003.4893	$1,003.49	$1,003.50	$1,003.50