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	$59.64	7.534%	$64.1333	$64.13	$64.15	$64.10
Purchase #2	$58.57	13.856%	$66.6855	$66.69	$66.70	$66.70
Purchase #3	$180.89	10.848%	$200.5129	$200.51	$200.50	$200.50
Purchase #4	$80.52	11.872%	$90.0793	$90.08	$90.10	$90.10
Purchase #5	$217.60	3.745%	$225.7491	$225.75	$225.75	$225.70
Purchase #6	$154.61	3.626%	$160.2162	$160.22	$160.20	$160.20
Purchase #7	$18.33	12.204%	$20.567	$20.57	$20.55	$20.60
7 purchase totals =	$770.16		$827.9433	$827.95	$827.95	$827.90