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	$10.78	10.265%	$11.8866	$11.89	$11.90	$11.90
Purchase #2	$77.50	6.464%	$82.5096	$82.51	$82.50	$82.50
Purchase #3	$242.45	4.356%	$253.0111	$253.01	$253.00	$253.00
Purchase #4	$25.80	12.115%	$28.9257	$28.93	$28.95	$28.90
Purchase #5	$150.40	13.187%	$170.2332	$170.23	$170.25	$170.20
Purchase #6	$21.82	8.416%	$23.6564	$23.66	$23.65	$23.70
Purchase #7	$102.38	6.694%	$109.2333	$109.23	$109.25	$109.20
7 purchase totals =	$631.13		$679.4559	$679.46	$679.50	$679.40