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	$79.47	4.279%	$82.8705	$82.87	$82.85	$82.90
Purchase #2	$241.51	6.750%	$257.8119	$257.81	$257.80	$257.80
Purchase #3	$42.90	12.428%	$48.2316	$48.23	$48.25	$48.20
Purchase #4	$234.62	8.870%	$255.4308	$255.43	$255.45	$255.40
Purchase #5	$34.51	8.222%	$37.3474	$37.35	$37.35	$37.30
Purchase #6	$199.90	6.724%	$213.3413	$213.34	$213.35	$213.30
Purchase #7	$50.70	6.464%	$53.9772	$53.98	$54.00	$54.00
7 purchase totals =	$883.61		$949.0107	$949.01	$949.05	$948.90