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	$40.45	5.563%	$42.7002	$42.70	$42.70	$42.70
Purchase #2	$242.56	10.291%	$267.5218	$267.52	$267.50	$267.50
Purchase #3	$122.78	5.161%	$129.1167	$129.12	$129.10	$129.10
Purchase #4	$64.69	6.126%	$68.6529	$68.65	$68.65	$68.70
Purchase #5	$172.88	13.437%	$196.1099	$196.11	$196.10	$196.10
Purchase #6	$227.56	5.574%	$240.2442	$240.24	$240.25	$240.20
Purchase #7	$133.93	6.309%	$142.3796	$142.38	$142.40	$142.40
7 purchase totals =	$1,004.85		$1,086.7253	$1,086.72	$1,086.70	$1,086.70