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	$37.43	13.512%	$42.4875	$42.49	$42.50	$42.50
Purchase #2	$115.81	7.260%	$124.2178	$124.22	$124.20	$124.20
Purchase #3	$248.64	5.567%	$262.4818	$262.48	$262.50	$262.50
Purchase #4	$190.72	12.802%	$215.136	$215.14	$215.15	$215.10
Purchase #5	$155.48	13.627%	$176.6673	$176.67	$176.65	$176.70
Purchase #6	$184.80	4.375%	$192.885	$192.89	$192.90	$192.90
Purchase #7	$128.89	7.355%	$138.3699	$138.37	$138.35	$138.40
7 purchase totals =	$1,061.77		$1,152.2453	$1,152.26	$1,152.25	$1,152.30