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	$17.81	13.708%	$20.2514	$20.25	$20.25	$20.30
Purchase #2	$87.52	3.389%	$90.4861	$90.49	$90.50	$90.50
Purchase #3	$38.47	8.858%	$41.8777	$41.88	$41.90	$41.90
Purchase #4	$170.57	9.338%	$186.4978	$186.50	$186.50	$186.50
Purchase #5	$126.87	7.280%	$136.1061	$136.11	$136.10	$136.10
Purchase #6	$28.59	13.720%	$32.5125	$32.51	$32.50	$32.50
Purchase #7	$82.57	8.596%	$89.6677	$89.67	$89.65	$89.70
7 purchase totals =	$552.40		$597.3993	$597.41	$597.40	$597.50