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	$87.78	10.638%	$97.118	$97.12	$97.10	$97.10
Purchase #2	$72.28	8.426%	$78.3703	$78.37	$78.35	$78.40
Purchase #3	$35.99	12.102%	$40.3455	$40.35	$40.35	$40.30
Purchase #4	$131.88	9.405%	$144.2833	$144.28	$144.30	$144.30
Purchase #5	$218.69	3.864%	$227.1402	$227.14	$227.15	$227.10
Purchase #6	$206.37	13.838%	$234.9275	$234.93	$234.95	$234.90
Purchase #7	$174.56	9.188%	$190.5986	$190.60	$190.60	$190.60
7 purchase totals =	$927.55		$1,012.7834	$1,012.79	$1,012.80	$1,012.70