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	$105.25	8.247%	$113.93	$113.93	$113.95	$113.90
Purchase #2	$83.44	9.435%	$91.3126	$91.31	$91.30	$91.30
Purchase #3	$119.88	10.159%	$132.0586	$132.06	$132.05	$132.10
Purchase #4	$177.41	3.303%	$183.2699	$183.27	$183.25	$183.30
Purchase #5	$156.80	5.831%	$165.943	$165.94	$165.95	$165.90
Purchase #6	$101.59	3.216%	$104.8571	$104.86	$104.85	$104.90
Purchase #7	$44.68	7.714%	$48.1266	$48.13	$48.15	$48.10
7 purchase totals =	$789.05		$839.4978	$839.50	$839.50	$839.50