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	$242.66	4.115%	$252.6455	$252.65	$252.65	$252.60
Purchase #2	$102.59	6.488%	$109.246	$109.25	$109.25	$109.20
Purchase #3	$78.58	7.645%	$84.5874	$84.59	$84.60	$84.60
Purchase #4	$74.99	4.743%	$78.5468	$78.55	$78.55	$78.50
Purchase #5	$35.43	5.244%	$37.2879	$37.29	$37.30	$37.30
Purchase #6	$33.37	6.665%	$35.5941	$35.59	$35.60	$35.60
Purchase #7	$16.68	7.348%	$17.9056	$17.91	$17.90	$17.90
7 purchase totals =	$584.30		$615.8133	$615.83	$615.85	$615.70