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	$83.33	7.535%	$89.6089	$89.61	$89.60	$89.60
Purchase #2	$98.92	4.730%	$103.5989	$103.60	$103.60	$103.60
Purchase #3	$230.86	7.612%	$248.4331	$248.43	$248.45	$248.40
Purchase #4	$216.67	3.647%	$224.572	$224.57	$224.55	$224.60
Purchase #5	$193.72	11.215%	$215.4457	$215.45	$215.45	$215.40
Purchase #6	$240.29	7.301%	$257.8336	$257.83	$257.85	$257.80
Purchase #7	$78.80	9.579%	$86.3483	$86.35	$86.35	$86.30
7 purchase totals =	$1,142.59		$1,225.8405	$1,225.84	$1,225.85	$1,225.70