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	$19.85	5.531%	$20.9479	$20.95	$20.95	$20.90
Purchase #2	$36.44	4.583%	$38.11	$38.11	$38.10	$38.10
Purchase #3	$77.37	5.311%	$81.4791	$81.48	$81.50	$81.50
Purchase #4	$72.29	7.210%	$77.5021	$77.50	$77.50	$77.50
Purchase #5	$86.49	3.836%	$89.8078	$89.81	$89.80	$89.80
Purchase #6	$105.54	7.218%	$113.1579	$113.16	$113.15	$113.20
Purchase #7	$183.34	12.105%	$205.5333	$205.53	$205.55	$205.50
7 purchase totals =	$581.32		$626.5381	$626.54	$626.55	$626.50