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	$140.53	10.288%	$154.9877	$154.99	$155.00	$155.00
Purchase #2	$110.72	11.605%	$123.5691	$123.57	$123.55	$123.60
Purchase #3	$149.77	10.688%	$165.7774	$165.78	$165.80	$165.80
Purchase #4	$139.43	8.281%	$150.9762	$150.98	$151.00	$151.00
Purchase #5	$31.52	9.149%	$34.4038	$34.40	$34.40	$34.40
Purchase #6	$78.89	9.320%	$86.2425	$86.24	$86.25	$86.20
Purchase #7	$45.76	13.326%	$51.858	$51.86	$51.85	$51.90
7 purchase totals =	$696.62		$767.8147	$767.82	$767.85	$767.90