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	$139.78	8.183%	$151.2182	$151.22	$151.20	$151.20
Purchase #2	$249.80	13.111%	$282.5513	$282.55	$282.55	$282.60
Purchase #3	$92.56	10.398%	$102.1844	$102.18	$102.20	$102.20
Purchase #4	$153.83	11.428%	$171.4097	$171.41	$171.40	$171.40
Purchase #5	$43.76	7.514%	$47.0481	$47.05	$47.05	$47.00
Purchase #6	$165.96	4.754%	$173.8497	$173.85	$173.85	$173.80
Purchase #7	$51.56	7.549%	$55.4523	$55.45	$55.45	$55.50
7 purchase totals =	$897.25		$983.7137	$983.71	$983.70	$983.70