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	$47.84	8.506%	$51.9093	$51.91	$51.90	$51.90
Purchase #2	$235.84	12.745%	$265.8978	$265.90	$265.90	$265.90
Purchase #3	$37.39	7.308%	$40.1225	$40.12	$40.10	$40.10
Purchase #4	$60.89	7.354%	$65.3679	$65.37	$65.35	$65.40
Purchase #5	$49.67	4.390%	$51.8505	$51.85	$51.85	$51.90
Purchase #6	$225.69	6.682%	$240.7706	$240.77	$240.75	$240.80
Purchase #7	$10.64	4.843%	$11.1553	$11.16	$11.15	$11.20
7 purchase totals =	$667.96		$727.0739	$727.08	$727.00	$727.20