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	$21.60	3.244%	$22.3007	$22.30	$22.30	$22.30
Purchase #2	$190.50	3.190%	$196.577	$196.58	$196.60	$196.60
Purchase #3	$93.55	8.845%	$101.8245	$101.82	$101.80	$101.80
Purchase #4	$98.80	13.533%	$112.1706	$112.17	$112.15	$112.20
Purchase #5	$42.27	6.292%	$44.9296	$44.93	$44.95	$44.90
Purchase #6	$66.71	8.696%	$72.5111	$72.51	$72.50	$72.50
Purchase #7	$135.68	5.106%	$142.6078	$142.61	$142.60	$142.60
7 purchase totals =	$649.11		$692.9213	$692.92	$692.90	$692.90