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	$156.29	10.656%	$172.9443	$172.94	$172.95	$172.90
Purchase #2	$135.54	3.406%	$140.1565	$140.16	$140.15	$140.20
Purchase #3	$141.81	10.575%	$156.8064	$156.81	$156.80	$156.80
Purchase #4	$207.52	13.331%	$235.1845	$235.18	$235.20	$235.20
Purchase #5	$169.46	10.685%	$187.5668	$187.57	$187.55	$187.60
Purchase #6	$85.49	5.779%	$90.4305	$90.43	$90.45	$90.40
Purchase #7	$227.71	7.474%	$244.729	$244.73	$244.75	$244.70
7 purchase totals =	$1,123.82		$1,227.8180	$1,227.82	$1,227.85	$1,227.80