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	$55.65	12.234%	$62.4582	$62.46	$62.45	$62.50
Purchase #2	$175.66	7.429%	$188.7098	$188.71	$188.70	$188.70
Purchase #3	$68.36	10.402%	$75.4708	$75.47	$75.45	$75.50
Purchase #4	$106.93	10.862%	$118.5447	$118.54	$118.55	$118.50
Purchase #5	$243.97	4.558%	$255.0902	$255.09	$255.10	$255.10
Purchase #6	$29.52	10.322%	$32.5671	$32.57	$32.55	$32.60
Purchase #7	$112.82	3.571%	$116.8488	$116.85	$116.85	$116.80
7 purchase totals =	$792.91		$849.6896	$849.69	$849.65	$849.70