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	$63.48	7.731%	$68.3876	$68.39	$68.40	$68.40
Purchase #2	$72.53	8.814%	$78.9228	$78.92	$78.90	$78.90
Purchase #3	$248.33	3.125%	$256.0903	$256.09	$256.10	$256.10
Purchase #4	$69.76	7.250%	$74.8176	$74.82	$74.80	$74.80
Purchase #5	$74.53	5.228%	$78.4264	$78.43	$78.45	$78.40
Purchase #6	$78.49	11.753%	$87.7149	$87.71	$87.70	$87.70
Purchase #7	$205.73	9.592%	$225.4636	$225.46	$225.45	$225.50
7 purchase totals =	$812.85		$869.8232	$869.82	$869.80	$869.80