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	$248.70	8.768%	$270.506	$270.51	$270.50	$270.50
Purchase #2	$203.81	12.837%	$229.9731	$229.97	$229.95	$230.00
Purchase #3	$212.34	7.209%	$227.6476	$227.65	$227.65	$227.60
Purchase #4	$130.63	9.277%	$142.7485	$142.75	$142.75	$142.70
Purchase #5	$38.73	4.864%	$40.6138	$40.61	$40.60	$40.60
Purchase #6	$48.91	3.260%	$50.5045	$50.50	$50.50	$50.50
Purchase #7	$40.32	5.550%	$42.5578	$42.56	$42.55	$42.60
7 purchase totals =	$923.44		$1,004.5513	$1,004.55	$1,004.50	$1,004.50