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	$5.34	3.267%	$5.5145	$5.51	$5.50	$5.50
Purchase #2	$207.43	10.477%	$229.1624	$229.16	$229.15	$229.20
Purchase #3	$169.78	11.208%	$188.8089	$188.81	$188.80	$188.80
Purchase #4	$131.89	12.850%	$148.8379	$148.84	$148.85	$148.80
Purchase #5	$45.58	13.192%	$51.5929	$51.59	$51.60	$51.60
Purchase #6	$27.27	8.415%	$29.5648	$29.56	$29.55	$29.60
Purchase #7	$173.54	5.286%	$182.7133	$182.71	$182.70	$182.70
7 purchase totals =	$760.83		$836.1947	$836.18	$836.15	$836.20