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	$90.79	5.224%	$95.5329	$95.53	$95.55	$95.50
Purchase #2	$95.65	7.455%	$102.7807	$102.78	$102.80	$102.80
Purchase #3	$96.83	13.130%	$109.5438	$109.54	$109.55	$109.50
Purchase #4	$111.83	10.466%	$123.5341	$123.53	$123.55	$123.50
Purchase #5	$50.25	13.412%	$56.9895	$56.99	$57.00	$57.00
Purchase #6	$122.48	10.613%	$135.4788	$135.48	$135.50	$135.50
Purchase #7	$163.97	6.690%	$174.9396	$174.94	$174.95	$174.90
7 purchase totals =	$731.80		$798.7994	$798.79	$798.90	$798.70