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	$26.37	9.710%	$28.9305	$28.93	$28.95	$28.90
Purchase #2	$163.40	4.286%	$170.4033	$170.40	$170.40	$170.40
Purchase #3	$40.83	9.758%	$44.8142	$44.81	$44.80	$44.80
Purchase #4	$82.99	7.826%	$89.4848	$89.48	$89.50	$89.50
Purchase #5	$131.70	4.367%	$137.4513	$137.45	$137.45	$137.50
Purchase #6	$238.26	5.173%	$250.5852	$250.59	$250.60	$250.60
Purchase #7	$150.93	9.810%	$165.7362	$165.74	$165.75	$165.70
7 purchase totals =	$834.48		$887.4055	$887.40	$887.45	$887.40