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	$230.74	4.353%	$240.7841	$240.78	$240.80	$240.80
Purchase #2	$86.77	9.183%	$94.7381	$94.74	$94.75	$94.70
Purchase #3	$90.56	10.332%	$99.9167	$99.92	$99.90	$99.90
Purchase #4	$66.95	8.403%	$72.5758	$72.58	$72.60	$72.60
Purchase #5	$223.46	9.680%	$245.0909	$245.09	$245.10	$245.10
Purchase #6	$189.78	10.285%	$209.2989	$209.30	$209.30	$209.30
Purchase #7	$67.82	4.538%	$70.8977	$70.90	$70.90	$70.90
7 purchase totals =	$956.08		$1,033.3022	$1,033.31	$1,033.35	$1,033.30