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	$229.76	4.391%	$239.8488	$239.85	$239.85	$239.80
Purchase #2	$52.47	4.482%	$54.8217	$54.82	$54.80	$54.80
Purchase #3	$127.52	12.288%	$143.1897	$143.19	$143.20	$143.20
Purchase #4	$223.57	6.543%	$238.1982	$238.20	$238.20	$238.20
Purchase #5	$176.68	13.544%	$200.6095	$200.61	$200.60	$200.60
Purchase #6	$243.51	13.315%	$275.9334	$275.93	$275.95	$275.90
Purchase #7	$169.90	9.252%	$185.6191	$185.62	$185.60	$185.60
7 purchase totals =	$1,223.41		$1,338.2204	$1,338.22	$1,338.20	$1,338.10