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	$100.71	5.723%	$106.4736	$106.47	$106.45	$106.50
Purchase #2	$198.60	10.215%	$218.887	$218.89	$218.90	$218.90
Purchase #3	$77.53	13.616%	$88.0865	$88.09	$88.10	$88.10
Purchase #4	$31.54	13.745%	$35.8752	$35.88	$35.90	$35.90
Purchase #5	$100.63	4.625%	$105.2841	$105.28	$105.30	$105.30
Purchase #6	$57.63	7.416%	$61.9038	$61.90	$61.90	$61.90
Purchase #7	$102.40	6.205%	$108.7539	$108.75	$108.75	$108.80
7 purchase totals =	$669.04		$725.2641	$725.26	$725.30	$725.40