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	$20.32	12.692%	$22.899	$22.90	$22.90	$22.90
Purchase #2	$219.85	13.214%	$248.901	$248.90	$248.90	$248.90
Purchase #3	$155.89	5.314%	$164.174	$164.17	$164.15	$164.20
Purchase #4	$60.61	11.353%	$67.4911	$67.49	$67.50	$67.50
Purchase #5	$216.97	11.371%	$241.6417	$241.64	$241.65	$241.60
Purchase #6	$51.39	5.468%	$54.2	$54.20	$54.20	$54.20
Purchase #7	$74.29	5.278%	$78.211	$78.21	$78.20	$78.20
7 purchase totals =	$799.32		$877.5178	$877.51	$877.50	$877.50