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	$140.59	11.482%	$156.7325	$156.73	$156.75	$156.70
Purchase #2	$131.68	7.444%	$141.4823	$141.48	$141.50	$141.50
Purchase #3	$123.97	12.243%	$139.1476	$139.15	$139.15	$139.10
Purchase #4	$146.83	10.361%	$162.0431	$162.04	$162.05	$162.00
Purchase #5	$48.30	7.715%	$52.0263	$52.03	$52.05	$52.00
Purchase #6	$195.65	12.179%	$219.4782	$219.48	$219.50	$219.50
Purchase #7	$100.38	11.360%	$111.7832	$111.78	$111.80	$111.80
7 purchase totals =	$887.40		$982.6932	$982.69	$982.80	$982.60