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	$127.78	6.689%	$136.3272	$136.33	$136.35	$136.30
Purchase #2	$183.41	9.103%	$200.1058	$200.11	$200.10	$200.10
Purchase #3	$70.26	12.296%	$78.8992	$78.90	$78.90	$78.90
Purchase #4	$250.59	7.660%	$269.7852	$269.79	$269.80	$269.80
Purchase #5	$142.98	6.579%	$152.3867	$152.39	$152.40	$152.40
Purchase #6	$214.32	9.748%	$235.2119	$235.21	$235.20	$235.20
Purchase #7	$42.62	3.586%	$44.1484	$44.15	$44.15	$44.10
7 purchase totals =	$1,031.96		$1,116.8644	$1,116.88	$1,116.90	$1,116.80