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	$50.56	12.136%	$56.696	$56.70	$56.70	$56.70
Purchase #2	$190.99	11.682%	$213.3015	$213.30	$213.30	$213.30
Purchase #3	$93.25	10.383%	$102.9321	$102.93	$102.95	$102.90
Purchase #4	$68.90	13.288%	$78.0554	$78.06	$78.05	$78.10
Purchase #5	$128.81	10.129%	$141.8572	$141.86	$141.85	$141.90
Purchase #6	$202.37	12.564%	$227.7958	$227.80	$227.80	$227.80
Purchase #7	$180.59	8.410%	$195.7776	$195.78	$195.80	$195.80
7 purchase totals =	$915.47		$1,016.4156	$1,016.43	$1,016.45	$1,016.50