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	$54.34	6.757%	$58.0118	$58.01	$58.00	$58.00
Purchase #2	$49.53	8.765%	$53.8713	$53.87	$53.85	$53.90
Purchase #3	$88.61	8.688%	$96.3084	$96.31	$96.30	$96.30
Purchase #4	$20.57	9.800%	$22.5859	$22.59	$22.60	$22.60
Purchase #5	$174.37	5.451%	$183.8749	$183.87	$183.85	$183.90
Purchase #6	$35.94	4.826%	$37.6745	$37.67	$37.65	$37.70
Purchase #7	$66.68	7.156%	$71.4516	$71.45	$71.45	$71.50
7 purchase totals =	$490.04		$523.7784	$523.77	$523.70	$523.90