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	$90.95	13.592%	$103.3119	$103.31	$103.30	$103.30
Purchase #2	$169.54	7.264%	$181.8554	$181.86	$181.85	$181.90
Purchase #3	$166.29	10.213%	$183.2732	$183.27	$183.25	$183.30
Purchase #4	$101.46	4.496%	$106.0216	$106.02	$106.00	$106.00
Purchase #5	$54.54	3.236%	$56.3049	$56.30	$56.30	$56.30
Purchase #6	$164.66	10.776%	$182.4038	$182.40	$182.40	$182.40
Purchase #7	$191.44	7.367%	$205.5434	$205.54	$205.55	$205.50
7 purchase totals =	$938.88		$1,018.7142	$1,018.70	$1,018.65	$1,018.70