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	$176.59	7.143%	$189.2038	$189.20	$189.20	$189.20
Purchase #2	$41.51	3.258%	$42.8624	$42.86	$42.85	$42.90
Purchase #3	$154.43	6.629%	$164.6672	$164.67	$164.65	$164.70
Purchase #4	$71.39	5.241%	$75.1315	$75.13	$75.15	$75.10
Purchase #5	$29.50	13.615%	$33.5164	$33.52	$33.50	$33.50
Purchase #6	$154.62	6.529%	$164.7151	$164.72	$164.70	$164.70
Purchase #7	$7.51	13.142%	$8.497	$8.50	$8.50	$8.50
7 purchase totals =	$635.55		$678.5934	$678.60	$678.55	$678.60