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	$36.66	10.229%	$40.41	$40.41	$40.40	$40.40
Purchase #2	$165.59	13.819%	$188.4729	$188.47	$188.45	$188.50
Purchase #3	$122.79	9.586%	$134.5606	$134.56	$134.55	$134.60
Purchase #4	$48.94	10.446%	$54.0523	$54.05	$54.05	$54.10
Purchase #5	$138.77	13.798%	$157.9175	$157.92	$157.90	$157.90
Purchase #6	$154.45	11.654%	$172.4496	$172.45	$172.45	$172.40
Purchase #7	$233.85	5.598%	$246.9409	$246.94	$246.95	$246.90
7 purchase totals =	$901.05		$994.8038	$994.80	$994.75	$994.80