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	$29.82	13.810%	$33.9381	$33.94	$33.95	$33.90
Purchase #2	$83.44	6.704%	$89.0338	$89.03	$89.05	$89.00
Purchase #3	$153.37	12.496%	$172.5351	$172.54	$172.55	$172.50
Purchase #4	$100.49	6.643%	$107.1656	$107.17	$107.15	$107.20
Purchase #5	$124.36	8.396%	$134.8013	$134.80	$134.80	$134.80
Purchase #6	$39.67	7.820%	$42.7722	$42.77	$42.75	$42.80
Purchase #7	$244.74	10.689%	$270.9003	$270.90	$270.90	$270.90
7 purchase totals =	$775.89		$851.1464	$851.15	$851.15	$851.10