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	$204.53	7.332%	$219.5261	$219.53	$219.55	$219.50
Purchase #2	$207.59	11.457%	$231.3736	$231.37	$231.35	$231.40
Purchase #3	$31.53	7.609%	$33.9291	$33.93	$33.95	$33.90
Purchase #4	$149.40	6.293%	$158.8017	$158.80	$158.80	$158.80
Purchase #5	$70.90	10.617%	$78.4275	$78.43	$78.45	$78.40
Purchase #6	$162.86	4.457%	$170.1187	$170.12	$170.10	$170.10
Purchase #7	$18.89	11.634%	$21.0877	$21.09	$21.10	$21.10
7 purchase totals =	$845.70		$913.2644	$913.27	$913.30	$913.20