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	$242.90	12.642%	$273.6074	$273.61	$273.60	$273.60
Purchase #2	$223.47	9.594%	$244.9097	$244.91	$244.90	$244.90
Purchase #3	$42.76	11.609%	$47.724	$47.72	$47.70	$47.70
Purchase #4	$72.74	8.471%	$78.9018	$78.90	$78.90	$78.90
Purchase #5	$208.35	6.446%	$221.7802	$221.78	$221.80	$221.80
Purchase #6	$105.59	8.405%	$114.4648	$114.46	$114.45	$114.50
Purchase #7	$223.27	5.827%	$236.2799	$236.28	$236.30	$236.30
7 purchase totals =	$1,119.08		$1,217.6678	$1,217.66	$1,217.65	$1,217.70