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	$249.90	8.686%	$271.6063	$271.61	$271.60	$271.60
Purchase #2	$129.46	7.721%	$139.4556	$139.46	$139.45	$139.50
Purchase #3	$50.48	10.712%	$55.8874	$55.89	$55.90	$55.90
Purchase #4	$123.37	8.585%	$133.9613	$133.96	$133.95	$134.00
Purchase #5	$32.49	10.376%	$35.8612	$35.86	$35.85	$35.90
Purchase #6	$10.90	4.608%	$11.4023	$11.40	$11.40	$11.40
Purchase #7	$43.73	3.724%	$45.3585	$45.36	$45.35	$45.40
7 purchase totals =	$640.33		$693.5326	$693.54	$693.50	$693.70