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	$75.99	3.320%	$78.5129	$78.51	$78.50	$78.50
Purchase #2	$119.98	5.155%	$126.165	$126.17	$126.15	$126.20
Purchase #3	$38.88	10.245%	$42.8633	$42.86	$42.85	$42.90
Purchase #4	$64.29	10.176%	$70.8322	$70.83	$70.85	$70.80
Purchase #5	$250.54	12.820%	$282.6592	$282.66	$282.65	$282.70
Purchase #6	$136.48	6.476%	$145.3184	$145.32	$145.30	$145.30
Purchase #7	$128.89	11.665%	$143.925	$143.93	$143.95	$143.90
7 purchase totals =	$815.05		$890.2760	$890.28	$890.25	$890.30