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	$140.43	9.509%	$153.7835	$153.78	$153.80	$153.80
Purchase #2	$99.59	4.236%	$103.8086	$103.81	$103.80	$103.80
Purchase #3	$34.40	6.305%	$36.5689	$36.57	$36.55	$36.60
Purchase #4	$65.87	9.102%	$71.8655	$71.87	$71.85	$71.90
Purchase #5	$92.79	11.486%	$103.4479	$103.45	$103.45	$103.40
Purchase #6	$193.51	11.129%	$215.0457	$215.05	$215.05	$215.00
Purchase #7	$250.32	10.224%	$275.9127	$275.91	$275.90	$275.90
7 purchase totals =	$876.91		$960.4328	$960.44	$960.40	$960.40