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	$17.55	5.221%	$18.4663	$18.47	$18.45	$18.50
Purchase #2	$127.33	4.396%	$132.9274	$132.93	$132.95	$132.90
Purchase #3	$41.97	3.143%	$43.2891	$43.29	$43.30	$43.30
Purchase #4	$240.80	13.397%	$273.06	$273.06	$273.05	$273.10
Purchase #5	$48.88	12.295%	$54.8898	$54.89	$54.90	$54.90
Purchase #6	$19.45	6.540%	$20.722	$20.72	$20.70	$20.70
Purchase #7	$221.50	3.820%	$229.9613	$229.96	$229.95	$230.00
7 purchase totals =	$717.48		$773.3159	$773.32	$773.30	$773.40