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	$99.43	5.326%	$104.7256	$104.73	$104.75	$104.70
Purchase #2	$186.78	7.408%	$200.6167	$200.62	$200.60	$200.60
Purchase #3	$178.62	12.398%	$200.7653	$200.77	$200.75	$200.80
Purchase #4	$209.38	4.596%	$219.0031	$219.00	$219.00	$219.00
Purchase #5	$26.34	3.864%	$27.3578	$27.36	$27.35	$27.40
Purchase #6	$55.30	13.209%	$62.6046	$62.60	$62.60	$62.60
Purchase #7	$71.55	8.221%	$77.4321	$77.43	$77.45	$77.40
7 purchase totals =	$827.40		$892.5052	$892.51	$892.50	$892.50