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	$128.73	13.269%	$145.8112	$145.81	$145.80	$145.80
Purchase #2	$104.90	5.824%	$111.0094	$111.01	$111.00	$111.00
Purchase #3	$225.39	11.322%	$250.9087	$250.91	$250.90	$250.90
Purchase #4	$171.64	4.663%	$179.6436	$179.64	$179.65	$179.60
Purchase #5	$46.59	3.530%	$48.2346	$48.23	$48.25	$48.20
Purchase #6	$102.26	8.769%	$111.2272	$111.23	$111.25	$111.20
Purchase #7	$247.99	12.708%	$279.5046	$279.50	$279.50	$279.50
7 purchase totals =	$1,027.50		$1,126.3393	$1,126.33	$1,126.35	$1,126.20