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	$147.65	7.338%	$158.4846	$158.48	$158.50	$158.50
Purchase #2	$91.26	12.311%	$102.495	$102.50	$102.50	$102.50
Purchase #3	$205.59	11.658%	$229.5577	$229.56	$229.55	$229.60
Purchase #4	$179.39	9.161%	$195.8239	$195.82	$195.80	$195.80
Purchase #5	$206.69	12.218%	$231.9434	$231.94	$231.95	$231.90
Purchase #6	$67.52	10.576%	$74.6609	$74.66	$74.65	$74.70
Purchase #7	$111.55	10.729%	$123.5182	$123.52	$123.50	$123.50
7 purchase totals =	$1,009.65		$1,116.4837	$1,116.48	$1,116.45	$1,116.50