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	$160.82	13.433%	$182.423	$182.42	$182.40	$182.40
Purchase #2	$101.78	12.593%	$114.5972	$114.60	$114.60	$114.60
Purchase #3	$191.83	3.383%	$198.3196	$198.32	$198.30	$198.30
Purchase #4	$10.61	3.522%	$10.9837	$10.98	$11.00	$11.00
Purchase #5	$30.88	6.742%	$32.9619	$32.96	$32.95	$33.00
Purchase #6	$86.25	5.198%	$90.7333	$90.73	$90.75	$90.70
Purchase #7	$114.78	12.338%	$128.9416	$128.94	$128.95	$128.90
7 purchase totals =	$696.95		$758.9603	$758.95	$758.95	$758.90