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	$11.47	3.310%	$11.8497	$11.85	$11.85	$11.80
Purchase #2	$31.45	4.665%	$32.9171	$32.92	$32.90	$32.90
Purchase #3	$28.34	3.856%	$29.4328	$29.43	$29.45	$29.40
Purchase #4	$128.41	9.423%	$140.5101	$140.51	$140.50	$140.50
Purchase #5	$106.71	8.247%	$115.5104	$115.51	$115.50	$115.50
Purchase #6	$20.61	10.515%	$22.7771	$22.78	$22.80	$22.80
Purchase #7	$42.83	4.242%	$44.6468	$44.65	$44.65	$44.60
7 purchase totals =	$369.82		$397.6440	$397.65	$397.65	$397.50