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	$17.76	12.155%	$19.9187	$19.92	$19.90	$19.90
Purchase #2	$245.85	11.243%	$273.4909	$273.49	$273.50	$273.50
Purchase #3	$24.89	12.522%	$28.0067	$28.01	$28.00	$28.00
Purchase #4	$230.76	11.218%	$256.6467	$256.65	$256.65	$256.60
Purchase #5	$210.41	6.106%	$223.2576	$223.26	$223.25	$223.30
Purchase #6	$18.47	10.507%	$20.4106	$20.41	$20.40	$20.40
Purchase #7	$83.75	3.796%	$86.9292	$86.93	$86.95	$86.90
7 purchase totals =	$831.89		$908.6604	$908.67	$908.65	$908.60