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	$26.33	9.217%	$28.7568	$28.76	$28.75	$28.80
Purchase #2	$186.78	5.287%	$196.6551	$196.66	$196.65	$196.70
Purchase #3	$47.32	9.724%	$51.9214	$51.92	$51.90	$51.90
Purchase #4	$160.69	7.102%	$172.1022	$172.10	$172.10	$172.10
Purchase #5	$100.34	3.208%	$103.5589	$103.56	$103.55	$103.60
Purchase #6	$162.31	13.235%	$183.7917	$183.79	$183.80	$183.80
Purchase #7	$149.66	13.579%	$169.9823	$169.98	$170.00	$170.00
7 purchase totals =	$833.43		$906.7684	$906.77	$906.75	$906.90