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	$229.77	4.765%	$240.7185	$240.72	$240.70	$240.70
Purchase #2	$37.56	11.817%	$41.9985	$42.00	$42.00	$42.00
Purchase #3	$59.54	10.244%	$65.6393	$65.64	$65.65	$65.60
Purchase #4	$151.89	6.256%	$161.3922	$161.39	$161.40	$161.40
Purchase #5	$130.31	9.487%	$142.6725	$142.67	$142.65	$142.70
Purchase #6	$56.83	11.137%	$63.1592	$63.16	$63.15	$63.20
Purchase #7	$16.80	12.406%	$18.8842	$18.88	$18.90	$18.90
7 purchase totals =	$682.70		$734.4644	$734.46	$734.45	$734.50