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	$26.69	13.738%	$30.3567	$30.36	$30.35	$30.40
Purchase #2	$177.36	10.790%	$196.4971	$196.50	$196.50	$196.50
Purchase #3	$39.39	11.544%	$43.9372	$43.94	$43.95	$43.90
Purchase #4	$198.39	12.335%	$222.8614	$222.86	$222.85	$222.90
Purchase #5	$68.38	9.539%	$74.9028	$74.90	$74.90	$74.90
Purchase #6	$118.64	5.167%	$124.7701	$124.77	$124.75	$124.80
Purchase #7	$169.42	6.590%	$180.5848	$180.58	$180.60	$180.60
7 purchase totals =	$798.27		$873.9101	$873.91	$873.90	$874.00