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	$247.40	13.326%	$280.3685	$280.37	$280.35	$280.40
Purchase #2	$164.67	8.517%	$178.6949	$178.69	$178.70	$178.70
Purchase #3	$20.27	6.346%	$21.5563	$21.56	$21.55	$21.60
Purchase #4	$37.39	5.439%	$39.4236	$39.42	$39.40	$39.40
Purchase #5	$159.78	8.829%	$173.887	$173.89	$173.90	$173.90
Purchase #6	$245.26	8.502%	$266.112	$266.11	$266.10	$266.10
Purchase #7	$32.84	10.584%	$36.3158	$36.32	$36.30	$36.30
7 purchase totals =	$907.61		$996.3581	$996.36	$996.30	$996.40