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	$23.67	11.497%	$26.3913	$26.39	$26.40	$26.40
Purchase #2	$175.93	7.743%	$189.5523	$189.55	$189.55	$189.60
Purchase #3	$46.72	11.156%	$51.9321	$51.93	$51.95	$51.90
Purchase #4	$35.74	4.619%	$37.3908	$37.39	$37.40	$37.40
Purchase #5	$82.76	7.805%	$89.2194	$89.22	$89.20	$89.20
Purchase #6	$142.32	11.431%	$158.5886	$158.59	$158.60	$158.60
Purchase #7	$52.85	10.471%	$58.3839	$58.38	$58.40	$58.40
7 purchase totals =	$559.99		$611.4584	$611.45	$611.50	$611.50