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	$37.36	5.368%	$39.3655	$39.37	$39.35	$39.40
Purchase #2	$35.34	7.611%	$38.0297	$38.03	$38.05	$38.00
Purchase #3	$215.29	6.122%	$228.4701	$228.47	$228.45	$228.50
Purchase #4	$250.68	3.629%	$259.7772	$259.78	$259.80	$259.80
Purchase #5	$17.82	9.619%	$19.5341	$19.53	$19.55	$19.50
Purchase #6	$37.88	10.731%	$41.9449	$41.94	$41.95	$41.90
Purchase #7	$165.66	4.665%	$173.388	$173.39	$173.40	$173.40
7 purchase totals =	$760.03		$800.5095	$800.51	$800.55	$800.50