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	$115.37	5.604%	$121.8353	$121.84	$121.85	$121.80
Purchase #2	$191.55	9.327%	$209.4159	$209.42	$209.40	$209.40
Purchase #3	$205.74	8.797%	$223.8389	$223.84	$223.85	$223.80
Purchase #4	$163.79	6.524%	$174.4757	$174.48	$174.50	$174.50
Purchase #5	$28.57	13.406%	$32.4001	$32.40	$32.40	$32.40
Purchase #6	$229.88	11.122%	$255.4473	$255.45	$255.45	$255.40
Purchase #7	$131.57	10.278%	$145.0928	$145.09	$145.10	$145.10
7 purchase totals =	$1,066.47		$1,162.5060	$1,162.52	$1,162.55	$1,162.40