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	$150.71	6.499%	$160.5046	$160.50	$160.50	$160.50
Purchase #2	$51.85	9.108%	$56.5725	$56.57	$56.55	$56.60
Purchase #3	$133.65	12.841%	$150.812	$150.81	$150.80	$150.80
Purchase #4	$86.99	11.302%	$96.8216	$96.82	$96.80	$96.80
Purchase #5	$61.66	7.608%	$66.3511	$66.35	$66.35	$66.40
Purchase #6	$127.72	11.535%	$142.4525	$142.45	$142.45	$142.50
Purchase #7	$12.56	3.190%	$12.9607	$12.96	$12.95	$13.00
7 purchase totals =	$625.14		$686.4750	$686.46	$686.40	$686.60