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	$218.42	7.404%	$234.5918	$234.59	$234.60	$234.60
Purchase #2	$169.95	11.732%	$189.8885	$189.89	$189.90	$189.90
Purchase #3	$49.82	13.206%	$56.3992	$56.40	$56.40	$56.40
Purchase #4	$165.73	12.694%	$186.7678	$186.77	$186.75	$186.80
Purchase #5	$168.35	3.416%	$174.1008	$174.10	$174.10	$174.10
Purchase #6	$92.87	13.403%	$105.3174	$105.32	$105.30	$105.30
Purchase #7	$26.89	10.827%	$29.8014	$29.80	$29.80	$29.80
7 purchase totals =	$892.03		$976.8669	$976.87	$976.85	$976.90