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	$37.92	11.770%	$42.3832	$42.38	$42.40	$42.40
Purchase #2	$17.33	4.604%	$18.1279	$18.13	$18.15	$18.10
Purchase #3	$224.39	12.864%	$253.2555	$253.26	$253.25	$253.30
Purchase #4	$233.57	6.680%	$249.1725	$249.17	$249.15	$249.20
Purchase #5	$193.89	6.710%	$206.9	$206.90	$206.90	$206.90
Purchase #6	$233.69	3.531%	$241.9416	$241.94	$241.95	$241.90
Purchase #7	$145.73	12.833%	$164.4315	$164.43	$164.45	$164.40
7 purchase totals =	$1,086.52		$1,176.2122	$1,176.21	$1,176.25	$1,176.20