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	$35.77	7.754%	$38.5436	$38.54	$38.55	$38.50
Purchase #2	$162.41	7.644%	$174.8246	$174.82	$174.80	$174.80
Purchase #3	$58.37	9.507%	$63.9192	$63.92	$63.90	$63.90
Purchase #4	$64.86	12.157%	$72.745	$72.75	$72.75	$72.70
Purchase #5	$248.61	5.863%	$263.186	$263.19	$263.20	$263.20
Purchase #6	$112.41	13.310%	$127.3718	$127.37	$127.35	$127.40
Purchase #7	$152.63	10.149%	$168.1204	$168.12	$168.10	$168.10
7 purchase totals =	$835.06		$908.7106	$908.71	$908.65	$908.60