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	$136.70	5.546%	$144.2814	$144.28	$144.30	$144.30
Purchase #2	$241.49	13.587%	$274.3012	$274.30	$274.30	$274.30
Purchase #3	$223.80	6.712%	$238.8215	$238.82	$238.80	$238.80
Purchase #4	$138.92	11.187%	$154.461	$154.46	$154.45	$154.50
Purchase #5	$53.65	10.436%	$59.2489	$59.25	$59.25	$59.20
Purchase #6	$113.99	13.569%	$129.4573	$129.46	$129.45	$129.50
Purchase #7	$124.89	12.414%	$140.3938	$140.39	$140.40	$140.40
7 purchase totals =	$1,033.44		$1,140.9651	$1,140.96	$1,140.95	$1,141.00