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	$69.78	4.331%	$72.8022	$72.80	$72.80	$72.80
Purchase #2	$99.33	5.526%	$104.819	$104.82	$104.80	$104.80
Purchase #3	$171.90	13.160%	$194.522	$194.52	$194.50	$194.50
Purchase #4	$76.52	3.678%	$79.3344	$79.33	$79.35	$79.30
Purchase #5	$56.81	5.269%	$59.8033	$59.80	$59.80	$59.80
Purchase #6	$177.60	3.835%	$184.411	$184.41	$184.40	$184.40
Purchase #7	$168.88	9.616%	$185.1195	$185.12	$185.10	$185.10
7 purchase totals =	$820.82		$880.8114	$880.80	$880.75	$880.70