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	$44.71	10.222%	$49.2803	$49.28	$49.30	$49.30
Purchase #2	$102.31	10.284%	$112.8316	$112.83	$112.85	$112.80
Purchase #3	$131.98	12.376%	$148.3138	$148.31	$148.30	$148.30
Purchase #4	$204.35	12.163%	$229.2051	$229.21	$229.20	$229.20
Purchase #5	$52.66	3.360%	$54.4294	$54.43	$54.45	$54.40
Purchase #6	$149.96	9.422%	$164.0892	$164.09	$164.10	$164.10
Purchase #7	$21.61	4.523%	$22.5874	$22.59	$22.60	$22.60
7 purchase totals =	$707.58		$780.7368	$780.74	$780.80	$780.70