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	$91.68	7.839%	$98.8668	$98.87	$98.85	$98.90
Purchase #2	$234.57	4.213%	$244.4524	$244.45	$244.45	$244.50
Purchase #3	$89.70	12.826%	$101.2049	$101.20	$101.20	$101.20
Purchase #4	$90.91	12.538%	$102.3083	$102.31	$102.30	$102.30
Purchase #5	$34.77	10.711%	$38.4942	$38.49	$38.50	$38.50
Purchase #6	$198.73	9.127%	$216.8681	$216.87	$216.85	$216.90
Purchase #7	$81.94	8.833%	$89.1778	$89.18	$89.20	$89.20
7 purchase totals =	$822.30		$891.3725	$891.37	$891.35	$891.50