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	$136.85	6.451%	$145.6782	$145.68	$145.70	$145.70
Purchase #2	$82.45	13.404%	$93.5016	$93.50	$93.50	$93.50
Purchase #3	$250.89	11.608%	$280.0133	$280.01	$280.00	$280.00
Purchase #4	$85.73	8.179%	$92.7419	$92.74	$92.75	$92.70
Purchase #5	$47.65	10.846%	$52.8181	$52.82	$52.80	$52.80
Purchase #6	$220.49	4.433%	$230.2643	$230.26	$230.25	$230.30
Purchase #7	$57.29	4.508%	$59.8726	$59.87	$59.85	$59.90
7 purchase totals =	$881.35		$954.8900	$954.88	$954.85	$954.90