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	$89.61	10.846%	$99.3291	$99.33	$99.35	$99.30
Purchase #2	$31.30	5.724%	$33.0916	$33.09	$33.10	$33.10
Purchase #3	$20.42	9.113%	$22.2809	$22.28	$22.30	$22.30
Purchase #4	$19.72	9.598%	$21.6127	$21.61	$21.60	$21.60
Purchase #5	$133.53	3.557%	$138.2797	$138.28	$138.30	$138.30
Purchase #6	$95.35	8.844%	$103.7828	$103.78	$103.80	$103.80
Purchase #7	$228.95	9.582%	$250.888	$250.89	$250.90	$250.90
7 purchase totals =	$618.88		$669.2648	$669.26	$669.35	$669.30