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	$60.67	11.320%	$67.5378	$67.54	$67.55	$67.50
Purchase #2	$114.96	7.326%	$123.382	$123.38	$123.40	$123.40
Purchase #3	$149.71	5.598%	$158.0908	$158.09	$158.10	$158.10
Purchase #4	$140.61	7.711%	$151.4524	$151.45	$151.45	$151.50
Purchase #5	$135.36	11.186%	$150.5014	$150.50	$150.50	$150.50
Purchase #6	$103.52	13.146%	$117.1287	$117.13	$117.15	$117.10
Purchase #7	$57.30	3.869%	$59.5169	$59.52	$59.50	$59.50
7 purchase totals =	$762.13		$827.6100	$827.61	$827.65	$827.60