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	$143.78	8.421%	$155.8877	$155.89	$155.90	$155.90
Purchase #2	$117.91	12.653%	$132.8292	$132.83	$132.85	$132.80
Purchase #3	$205.85	13.217%	$233.0572	$233.06	$233.05	$233.10
Purchase #4	$240.60	7.402%	$258.4092	$258.41	$258.40	$258.40
Purchase #5	$64.46	10.279%	$71.0858	$71.09	$71.10	$71.10
Purchase #6	$76.26	7.243%	$81.7835	$81.78	$81.80	$81.80
Purchase #7	$139.91	6.341%	$148.7817	$148.78	$148.80	$148.80
7 purchase totals =	$988.77		$1,081.8343	$1,081.84	$1,081.90	$1,081.90