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	$250.35	7.790%	$269.8523	$269.85	$269.85	$269.90
Purchase #2	$212.62	5.465%	$224.2397	$224.24	$224.25	$224.20
Purchase #3	$11.44	11.832%	$12.7936	$12.79	$12.80	$12.80
Purchase #4	$242.27	12.456%	$272.4472	$272.45	$272.45	$272.40
Purchase #5	$93.59	7.751%	$100.8442	$100.84	$100.85	$100.80
Purchase #6	$89.37	3.131%	$92.1682	$92.17	$92.15	$92.20
Purchase #7	$229.50	11.116%	$255.0112	$255.01	$255.00	$255.00
7 purchase totals =	$1,129.14		$1,227.3564	$1,227.35	$1,227.35	$1,227.30