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	$110.29	12.428%	$123.9968	$124.00	$124.00	$124.00
Purchase #2	$75.90	8.347%	$82.2354	$82.24	$82.25	$82.20
Purchase #3	$88.83	4.535%	$92.8584	$92.86	$92.85	$92.90
Purchase #4	$61.47	7.421%	$66.0317	$66.03	$66.05	$66.00
Purchase #5	$20.66	10.131%	$22.7531	$22.75	$22.75	$22.80
Purchase #6	$47.51	12.779%	$53.5813	$53.58	$53.60	$53.60
Purchase #7	$72.62	7.820%	$78.2989	$78.30	$78.30	$78.30
7 purchase totals =	$477.28		$519.7556	$519.76	$519.80	$519.80