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	$54.51	6.196%	$57.8874	$57.89	$57.90	$57.90
Purchase #2	$188.56	6.566%	$200.9408	$200.94	$200.95	$200.90
Purchase #3	$247.64	4.153%	$257.9245	$257.92	$257.90	$257.90
Purchase #4	$192.33	8.838%	$209.3281	$209.33	$209.35	$209.30
Purchase #5	$29.47	8.855%	$32.0796	$32.08	$32.10	$32.10
Purchase #6	$120.59	11.517%	$134.4784	$134.48	$134.50	$134.50
Purchase #7	$12.67	5.661%	$13.3872	$13.39	$13.40	$13.40
7 purchase totals =	$845.77		$906.0260	$906.03	$906.10	$906.00