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	$250.77	13.749%	$285.2484	$285.25	$285.25	$285.20
Purchase #2	$196.89	3.510%	$203.8008	$203.80	$203.80	$203.80
Purchase #3	$74.84	3.396%	$77.3816	$77.38	$77.40	$77.40
Purchase #4	$77.27	4.609%	$80.8314	$80.83	$80.85	$80.80
Purchase #5	$194.40	12.606%	$218.9061	$218.91	$218.90	$218.90
Purchase #6	$48.69	7.280%	$52.2346	$52.23	$52.25	$52.20
Purchase #7	$97.34	3.331%	$100.5824	$100.58	$100.60	$100.60
7 purchase totals =	$940.20		$1,018.9853	$1,018.98	$1,019.05	$1,018.90