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	$47.90	5.424%	$50.4981	$50.50	$50.50	$50.50
Purchase #2	$246.49	3.175%	$254.3161	$254.32	$254.30	$254.30
Purchase #3	$210.77	13.251%	$238.6991	$238.70	$238.70	$238.70
Purchase #4	$169.35	5.486%	$178.6405	$178.64	$178.65	$178.60
Purchase #5	$46.37	6.774%	$49.5111	$49.51	$49.50	$49.50
Purchase #6	$35.91	6.102%	$38.1012	$38.10	$38.10	$38.10
Purchase #7	$37.90	6.761%	$40.4624	$40.46	$40.45	$40.50
7 purchase totals =	$794.69		$850.2285	$850.23	$850.20	$850.20