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	$75.45	6.329%	$80.2252	$80.23	$80.25	$80.20
Purchase #2	$200.27	11.575%	$223.4513	$223.45	$223.45	$223.50
Purchase #3	$19.25	8.116%	$20.8123	$20.81	$20.80	$20.80
Purchase #4	$74.78	9.759%	$82.0778	$82.08	$82.10	$82.10
Purchase #5	$192.43	3.633%	$199.421	$199.42	$199.40	$199.40
Purchase #6	$234.95	11.808%	$262.6929	$262.69	$262.70	$262.70
Purchase #7	$145.90	7.843%	$157.3429	$157.34	$157.35	$157.30
7 purchase totals =	$943.03		$1,026.0234	$1,026.02	$1,026.05	$1,026.00