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	$209.91	6.339%	$223.2162	$223.22	$223.20	$223.20
Purchase #2	$90.96	10.577%	$100.5808	$100.58	$100.60	$100.60
Purchase #3	$5.54	4.228%	$5.7742	$5.77	$5.75	$5.80
Purchase #4	$77.46	6.755%	$82.6924	$82.69	$82.70	$82.70
Purchase #5	$247.26	3.332%	$255.4987	$255.50	$255.50	$255.50
Purchase #6	$80.67	10.592%	$89.2146	$89.21	$89.20	$89.20
Purchase #7	$214.66	11.834%	$240.0629	$240.06	$240.05	$240.10
7 purchase totals =	$926.46		$997.0398	$997.03	$997.00	$997.10