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	$35.54	7.403%	$38.171	$38.17	$38.15	$38.20
Purchase #2	$89.51	9.839%	$98.3169	$98.32	$98.30	$98.30
Purchase #3	$78.70	13.826%	$89.5811	$89.58	$89.60	$89.60
Purchase #4	$27.63	11.704%	$30.8638	$30.86	$30.85	$30.90
Purchase #5	$58.82	13.525%	$66.7754	$66.78	$66.80	$66.80
Purchase #6	$61.72	7.428%	$66.3046	$66.30	$66.30	$66.30
Purchase #7	$200.65	7.545%	$215.789	$215.79	$215.80	$215.80
7 purchase totals =	$552.57		$605.8018	$605.80	$605.80	$605.90