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	$90.41	10.860%	$100.2285	$100.23	$100.25	$100.20
Purchase #2	$93.28	11.295%	$103.816	$103.82	$103.80	$103.80
Purchase #3	$95.77	3.647%	$99.2627	$99.26	$99.25	$99.30
Purchase #4	$7.90	6.239%	$8.3929	$8.39	$8.40	$8.40
Purchase #5	$30.35	7.305%	$32.5671	$32.57	$32.55	$32.60
Purchase #6	$29.55	6.409%	$31.4439	$31.44	$31.45	$31.40
Purchase #7	$111.95	10.317%	$123.4999	$123.50	$123.50	$123.50
7 purchase totals =	$459.21		$499.2110	$499.21	$499.20	$499.20