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	$83.50	5.432%	$88.0357	$88.04	$88.05	$88.00
Purchase #2	$105.85	5.470%	$111.64	$111.64	$111.65	$111.60
Purchase #3	$67.47	7.382%	$72.4506	$72.45	$72.45	$72.50
Purchase #4	$214.56	9.712%	$235.3981	$235.40	$235.40	$235.40
Purchase #5	$45.80	3.234%	$47.2812	$47.28	$47.30	$47.30
Purchase #6	$72.77	5.556%	$76.8131	$76.81	$76.80	$76.80
Purchase #7	$34.71	7.383%	$37.2726	$37.27	$37.25	$37.30
7 purchase totals =	$624.66		$668.8913	$668.89	$668.90	$668.90