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	$30.63	10.609%	$33.8795	$33.88	$33.90	$33.90
Purchase #2	$209.89	13.455%	$238.1307	$238.13	$238.15	$238.10
Purchase #3	$230.40	10.763%	$255.198	$255.20	$255.20	$255.20
Purchase #4	$226.67	12.863%	$255.8266	$255.83	$255.85	$255.80
Purchase #5	$227.29	12.735%	$256.2354	$256.24	$256.25	$256.20
Purchase #6	$163.69	7.255%	$175.5657	$175.57	$175.55	$175.60
Purchase #7	$73.68	13.399%	$83.5524	$83.55	$83.55	$83.60
7 purchase totals =	$1,162.25		$1,298.3883	$1,298.40	$1,298.45	$1,298.40