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	$215.31	3.495%	$222.8351	$222.84	$222.85	$222.80
Purchase #2	$131.79	12.852%	$148.7277	$148.73	$148.75	$148.70
Purchase #3	$129.35	6.288%	$137.4835	$137.48	$137.50	$137.50
Purchase #4	$147.72	8.797%	$160.7149	$160.71	$160.70	$160.70
Purchase #5	$20.72	6.566%	$22.0805	$22.08	$22.10	$22.10
Purchase #6	$64.95	11.698%	$72.5479	$72.55	$72.55	$72.50
Purchase #7	$111.25	4.477%	$116.2307	$116.23	$116.25	$116.20
7 purchase totals =	$821.09		$880.6203	$880.62	$880.70	$880.50