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	$175.45	6.217%	$186.3577	$186.36	$186.35	$186.40
Purchase #2	$58.78	3.205%	$60.6639	$60.66	$60.65	$60.70
Purchase #3	$104.95	6.548%	$111.8221	$111.82	$111.80	$111.80
Purchase #4	$91.62	8.712%	$99.6019	$99.60	$99.60	$99.60
Purchase #5	$215.89	12.338%	$242.5265	$242.53	$242.55	$242.50
Purchase #6	$62.46	11.213%	$69.4636	$69.46	$69.45	$69.50
Purchase #7	$47.93	11.835%	$53.6025	$53.60	$53.60	$53.60
7 purchase totals =	$757.08		$824.0382	$824.03	$824.00	$824.10