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	$35.89	10.247%	$39.5676	$39.57	$39.55	$39.60
Purchase #2	$72.75	11.689%	$81.2537	$81.25	$81.25	$81.30
Purchase #3	$164.91	12.548%	$185.6029	$185.60	$185.60	$185.60
Purchase #4	$203.65	7.722%	$219.3759	$219.38	$219.40	$219.40
Purchase #5	$26.73	10.870%	$29.6356	$29.64	$29.65	$29.60
Purchase #6	$80.63	13.501%	$91.5159	$91.52	$91.50	$91.50
Purchase #7	$165.74	13.182%	$187.5878	$187.59	$187.60	$187.60
7 purchase totals =	$750.30		$834.5394	$834.55	$834.55	$834.60