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	$15.49	13.855%	$17.6361	$17.64	$17.65	$17.60
Purchase #2	$97.47	12.467%	$109.6216	$109.62	$109.60	$109.60
Purchase #3	$58.40	5.236%	$61.4578	$61.46	$61.45	$61.50
Purchase #4	$167.42	13.822%	$190.5608	$190.56	$190.55	$190.60
Purchase #5	$245.84	11.654%	$274.4902	$274.49	$274.50	$274.50
Purchase #6	$142.58	13.192%	$161.3892	$161.39	$161.40	$161.40
Purchase #7	$93.33	12.309%	$104.818	$104.82	$104.80	$104.80
7 purchase totals =	$820.53		$919.9737	$919.98	$919.95	$920.00