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	$185.65	3.181%	$191.5555	$191.56	$191.55	$191.60
Purchase #2	$143.49	12.266%	$161.0905	$161.09	$161.10	$161.10
Purchase #3	$244.79	11.646%	$273.2982	$273.30	$273.30	$273.30
Purchase #4	$44.48	5.426%	$46.8935	$46.89	$46.90	$46.90
Purchase #5	$107.90	3.298%	$111.4585	$111.46	$111.45	$111.50
Purchase #6	$19.93	4.762%	$20.8791	$20.88	$20.90	$20.90
Purchase #7	$52.53	9.661%	$57.6049	$57.60	$57.60	$57.60
7 purchase totals =	$798.77		$862.7802	$862.78	$862.80	$862.90