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	$10.35	3.404%	$10.7023	$10.70	$10.70	$10.70
Purchase #2	$81.41	12.825%	$91.8508	$91.85	$91.85	$91.90
Purchase #3	$90.79	9.406%	$99.3297	$99.33	$99.35	$99.30
Purchase #4	$208.50	3.341%	$215.466	$215.47	$215.45	$215.50
Purchase #5	$155.47	7.106%	$166.5177	$166.52	$166.50	$166.50
Purchase #6	$213.49	4.590%	$223.2892	$223.29	$223.30	$223.30
Purchase #7	$46.56	13.258%	$52.7329	$52.73	$52.75	$52.70
7 purchase totals =	$806.57		$859.8886	$859.89	$859.90	$859.90