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	$27.89	13.668%	$31.702	$31.70	$31.70	$31.70
Purchase #2	$200.66	9.685%	$220.0939	$220.09	$220.10	$220.10
Purchase #3	$162.81	5.415%	$171.6262	$171.63	$171.65	$171.60
Purchase #4	$137.74	3.680%	$142.8088	$142.81	$142.80	$142.80
Purchase #5	$87.38	13.813%	$99.4498	$99.45	$99.45	$99.40
Purchase #6	$224.81	6.546%	$239.5261	$239.53	$239.55	$239.50
Purchase #7	$179.52	11.756%	$200.6244	$200.62	$200.60	$200.60
7 purchase totals =	$1,020.81		$1,105.8312	$1,105.83	$1,105.85	$1,105.70