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	$142.55	12.606%	$160.5199	$160.52	$160.50	$160.50
Purchase #2	$194.93	9.608%	$213.6589	$213.66	$213.65	$213.70
Purchase #3	$57.42	3.807%	$59.606	$59.61	$59.60	$59.60
Purchase #4	$175.86	11.371%	$195.857	$195.86	$195.85	$195.90
Purchase #5	$93.30	3.766%	$96.8137	$96.81	$96.80	$96.80
Purchase #6	$39.55	10.428%	$43.6743	$43.67	$43.65	$43.70
Purchase #7	$79.70	11.646%	$88.9819	$88.98	$89.00	$89.00
7 purchase totals =	$783.31		$859.1117	$859.11	$859.05	$859.20