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	$244.94	10.294%	$270.1541	$270.15	$270.15	$270.20
Purchase #2	$218.83	13.808%	$249.046	$249.05	$249.05	$249.00
Purchase #3	$28.77	9.461%	$31.4919	$31.49	$31.50	$31.50
Purchase #4	$206.57	4.719%	$216.318	$216.32	$216.30	$216.30
Purchase #5	$126.52	4.199%	$131.8326	$131.83	$131.85	$131.80
Purchase #6	$164.72	10.178%	$181.4852	$181.49	$181.50	$181.50
Purchase #7	$104.41	7.707%	$112.4569	$112.46	$112.45	$112.50
7 purchase totals =	$1,094.76		$1,192.7847	$1,192.79	$1,192.80	$1,192.80