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	$139.43	5.492%	$147.0875	$147.09	$147.10	$147.10
Purchase #2	$180.66	7.710%	$194.5889	$194.59	$194.60	$194.60
Purchase #3	$98.34	9.512%	$107.6941	$107.69	$107.70	$107.70
Purchase #4	$71.52	9.742%	$78.4875	$78.49	$78.50	$78.50
Purchase #5	$130.71	9.643%	$143.3144	$143.31	$143.30	$143.30
Purchase #6	$42.34	10.227%	$46.6701	$46.67	$46.65	$46.70
Purchase #7	$79.92	3.803%	$82.9594	$82.96	$82.95	$83.00
7 purchase totals =	$742.92		$800.8019	$800.80	$800.80	$800.90