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	$249.89	11.256%	$278.0176	$278.02	$278.00	$278.00
Purchase #2	$139.87	4.483%	$146.1404	$146.14	$146.15	$146.10
Purchase #3	$118.76	7.723%	$127.9318	$127.93	$127.95	$127.90
Purchase #4	$214.54	4.256%	$223.6708	$223.67	$223.65	$223.70
Purchase #5	$82.87	3.791%	$86.0116	$86.01	$86.00	$86.00
Purchase #6	$102.40	12.242%	$114.9358	$114.94	$114.95	$114.90
Purchase #7	$96.69	7.602%	$104.0404	$104.04	$104.05	$104.00
7 purchase totals =	$1,005.02		$1,080.7484	$1,080.75	$1,080.75	$1,080.60