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	$110.63	10.611%	$122.3689	$122.37	$122.35	$122.40
Purchase #2	$40.62	4.338%	$42.3821	$42.38	$42.40	$42.40
Purchase #3	$202.28	10.111%	$222.7325	$222.73	$222.75	$222.70
Purchase #4	$98.50	5.686%	$104.1007	$104.10	$104.10	$104.10
Purchase #5	$72.50	10.450%	$80.0763	$80.08	$80.10	$80.10
Purchase #6	$143.42	7.307%	$153.8997	$153.90	$153.90	$153.90
Purchase #7	$74.69	4.770%	$78.2527	$78.25	$78.25	$78.30
7 purchase totals =	$742.64		$803.8129	$803.81	$803.85	$803.90