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	$72.60	9.191%	$79.2727	$79.27	$79.25	$79.30
Purchase #2	$185.90	5.711%	$196.5167	$196.52	$196.50	$196.50
Purchase #3	$80.43	7.632%	$86.5684	$86.57	$86.55	$86.60
Purchase #4	$33.73	4.460%	$35.2344	$35.23	$35.25	$35.20
Purchase #5	$112.93	4.190%	$117.6618	$117.66	$117.65	$117.70
Purchase #6	$130.84	10.384%	$144.4264	$144.43	$144.45	$144.40
Purchase #7	$35.44	9.545%	$38.8227	$38.82	$38.80	$38.80
7 purchase totals =	$651.87		$698.5031	$698.50	$698.45	$698.50