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	$127.68	12.274%	$143.3514	$143.35	$143.35	$143.40
Purchase #2	$40.81	13.125%	$46.1663	$46.17	$46.15	$46.20
Purchase #3	$229.48	4.185%	$239.0837	$239.08	$239.10	$239.10
Purchase #4	$213.41	9.585%	$233.8653	$233.87	$233.85	$233.90
Purchase #5	$63.45	13.635%	$72.1014	$72.10	$72.10	$72.10
Purchase #6	$18.98	8.173%	$20.5312	$20.53	$20.55	$20.50
Purchase #7	$168.50	8.161%	$182.2513	$182.25	$182.25	$182.30
7 purchase totals =	$862.31		$937.3506	$937.35	$937.35	$937.50