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	$79.63	12.232%	$89.3703	$89.37	$89.35	$89.40
Purchase #2	$67.66	6.777%	$72.2453	$72.25	$72.25	$72.20
Purchase #3	$136.88	13.178%	$154.918	$154.92	$154.90	$154.90
Purchase #4	$63.49	12.637%	$71.5132	$71.51	$71.50	$71.50
Purchase #5	$175.93	10.728%	$194.8038	$194.80	$194.80	$194.80
Purchase #6	$79.73	3.705%	$82.684	$82.68	$82.70	$82.70
Purchase #7	$121.33	9.387%	$132.7192	$132.72	$132.70	$132.70
7 purchase totals =	$724.65		$798.2538	$798.25	$798.20	$798.20