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	$179.75	4.680%	$188.1623	$188.16	$188.15	$188.20
Purchase #2	$93.88	12.800%	$105.8966	$105.90	$105.90	$105.90
Purchase #3	$220.73	3.158%	$227.7007	$227.70	$227.70	$227.70
Purchase #4	$11.66	13.584%	$13.2439	$13.24	$13.25	$13.20
Purchase #5	$37.66	13.719%	$42.8266	$42.83	$42.85	$42.80
Purchase #6	$126.43	13.173%	$143.0846	$143.08	$143.10	$143.10
Purchase #7	$236.40	11.419%	$263.3945	$263.39	$263.40	$263.40
7 purchase totals =	$906.51		$984.3092	$984.30	$984.35	$984.30