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	$90.48	12.167%	$101.4887	$101.49	$101.50	$101.50
Purchase #2	$83.82	5.296%	$88.2591	$88.26	$88.25	$88.30
Purchase #3	$150.81	9.311%	$164.8519	$164.85	$164.85	$164.90
Purchase #4	$53.90	8.761%	$58.6222	$58.62	$58.60	$58.60
Purchase #5	$113.83	12.419%	$127.9665	$127.97	$127.95	$128.00
Purchase #6	$99.43	4.380%	$103.785	$103.79	$103.80	$103.80
Purchase #7	$163.99	4.606%	$171.5434	$171.54	$171.55	$171.50
7 purchase totals =	$756.26		$816.5168	$816.52	$816.50	$816.60