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	$170.85	8.509%	$185.3876	$185.39	$185.40	$185.40
Purchase #2	$89.52	11.220%	$99.5641	$99.56	$99.55	$99.60
Purchase #3	$103.77	7.598%	$111.6544	$111.65	$111.65	$111.70
Purchase #4	$89.46	13.452%	$101.4942	$101.49	$101.50	$101.50
Purchase #5	$87.30	12.328%	$98.0623	$98.06	$98.05	$98.10
Purchase #6	$87.30	7.564%	$93.9034	$93.90	$93.90	$93.90
Purchase #7	$157.93	3.718%	$163.8018	$163.80	$163.80	$163.80
7 purchase totals =	$786.13		$853.8678	$853.85	$853.85	$854.00