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	$233.39	4.283%	$243.3861	$243.39	$243.40	$243.40
Purchase #2	$161.57	11.162%	$179.6044	$179.60	$179.60	$179.60
Purchase #3	$64.32	12.439%	$72.3208	$72.32	$72.30	$72.30
Purchase #4	$72.93	10.292%	$80.436	$80.44	$80.45	$80.40
Purchase #5	$15.78	9.489%	$17.2774	$17.28	$17.30	$17.30
Purchase #6	$16.89	12.484%	$18.9985	$19.00	$19.00	$19.00
Purchase #7	$39.75	5.672%	$42.0046	$42.00	$42.00	$42.00
7 purchase totals =	$604.63		$654.0278	$654.03	$654.05	$654.00