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	$82.48	9.810%	$90.5713	$90.57	$90.55	$90.60
Purchase #2	$56.62	5.354%	$59.6514	$59.65	$59.65	$59.70
Purchase #3	$250.94	13.414%	$284.6011	$284.60	$284.60	$284.60
Purchase #4	$181.54	8.636%	$197.2178	$197.22	$197.20	$197.20
Purchase #5	$122.57	5.103%	$128.8247	$128.82	$128.80	$128.80
Purchase #6	$40.51	7.304%	$43.4689	$43.47	$43.45	$43.50
Purchase #7	$226.70	10.268%	$249.9776	$249.98	$250.00	$250.00
7 purchase totals =	$961.36		$1,054.3128	$1,054.31	$1,054.25	$1,054.40