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	$240.39	7.228%	$257.7654	$257.77	$257.75	$257.80
Purchase #2	$162.75	5.555%	$171.7908	$171.79	$171.80	$171.80
Purchase #3	$107.83	3.487%	$111.59	$111.59	$111.60	$111.60
Purchase #4	$72.35	5.481%	$76.3155	$76.32	$76.30	$76.30
Purchase #5	$229.39	13.688%	$260.7889	$260.79	$260.80	$260.80
Purchase #6	$53.25	5.192%	$56.0147	$56.01	$56.00	$56.00
Purchase #7	$145.80	4.355%	$152.1496	$152.15	$152.15	$152.10
7 purchase totals =	$1,011.76		$1,086.4149	$1,086.42	$1,086.40	$1,086.40