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	$166.72	12.273%	$187.1815	$187.18	$187.20	$187.20
Purchase #2	$51.38	12.754%	$57.933	$57.93	$57.95	$57.90
Purchase #3	$131.57	4.489%	$137.4762	$137.48	$137.50	$137.50
Purchase #4	$111.25	10.626%	$123.0714	$123.07	$123.05	$123.10
Purchase #5	$35.26	4.464%	$36.834	$36.83	$36.85	$36.80
Purchase #6	$166.71	7.374%	$179.0032	$179.00	$179.00	$179.00
Purchase #7	$134.73	12.267%	$151.2573	$151.26	$151.25	$151.30
7 purchase totals =	$797.62		$872.7566	$872.75	$872.80	$872.80