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	$80.48	12.695%	$90.6969	$90.70	$90.70	$90.70
Purchase #2	$136.34	4.816%	$142.9061	$142.91	$142.90	$142.90
Purchase #3	$100.45	8.765%	$109.2544	$109.25	$109.25	$109.30
Purchase #4	$196.49	7.765%	$211.7474	$211.75	$211.75	$211.70
Purchase #5	$104.60	11.485%	$116.6133	$116.61	$116.60	$116.60
Purchase #6	$126.90	13.177%	$143.6216	$143.62	$143.60	$143.60
Purchase #7	$71.99	11.855%	$80.5244	$80.52	$80.50	$80.50
7 purchase totals =	$817.25		$895.3641	$895.36	$895.30	$895.30