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	$85.56	4.523%	$89.4299	$89.43	$89.45	$89.40
Purchase #2	$70.80	7.812%	$76.3309	$76.33	$76.35	$76.30
Purchase #3	$131.85	12.258%	$148.0122	$148.01	$148.00	$148.00
Purchase #4	$46.69	11.557%	$52.086	$52.09	$52.10	$52.10
Purchase #5	$11.33	13.518%	$12.8616	$12.86	$12.85	$12.90
Purchase #6	$41.28	7.293%	$44.2906	$44.29	$44.30	$44.30
Purchase #7	$128.75	13.389%	$145.9883	$145.99	$146.00	$146.00
7 purchase totals =	$516.26		$568.9995	$569.00	$569.05	$569.00