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	$19.92	4.834%	$20.8829	$20.88	$20.90	$20.90
Purchase #2	$77.53	4.626%	$81.1165	$81.12	$81.10	$81.10
Purchase #3	$49.25	12.592%	$55.4516	$55.45	$55.45	$55.50
Purchase #4	$34.44	9.371%	$37.6674	$37.67	$37.65	$37.70
Purchase #5	$194.31	3.373%	$200.8641	$200.86	$200.85	$200.90
Purchase #6	$38.83	8.723%	$42.2171	$42.22	$42.20	$42.20
Purchase #7	$20.41	8.867%	$22.2198	$22.22	$22.20	$22.20
7 purchase totals =	$434.69		$460.4194	$460.42	$460.35	$460.50