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	$220.78	13.397%	$250.3579	$250.36	$250.35	$250.40
Purchase #2	$158.86	9.611%	$174.128	$174.13	$174.15	$174.10
Purchase #3	$134.49	13.447%	$152.5749	$152.57	$152.55	$152.60
Purchase #4	$180.27	9.776%	$197.8932	$197.89	$197.90	$197.90
Purchase #5	$75.27	4.294%	$78.5021	$78.50	$78.50	$78.50
Purchase #6	$147.81	8.126%	$159.821	$159.82	$159.80	$159.80
Purchase #7	$62.88	5.399%	$66.2749	$66.27	$66.25	$66.30
7 purchase totals =	$980.36		$1,079.5520	$1,079.54	$1,079.50	$1,079.60