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	$121.45	8.337%	$131.5753	$131.58	$131.60	$131.60
Purchase #2	$211.50	13.864%	$240.8224	$240.82	$240.80	$240.80
Purchase #3	$39.81	7.737%	$42.8901	$42.89	$42.90	$42.90
Purchase #4	$60.80	4.277%	$63.4004	$63.40	$63.40	$63.40
Purchase #5	$192.76	3.851%	$200.1832	$200.18	$200.20	$200.20
Purchase #6	$135.66	12.692%	$152.878	$152.88	$152.90	$152.90
Purchase #7	$14.78	9.230%	$16.1442	$16.14	$16.15	$16.10
7 purchase totals =	$776.76		$847.8936	$847.89	$847.95	$847.90