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	$126.32	10.741%	$139.888	$139.89	$139.90	$139.90
Purchase #2	$229.63	11.284%	$255.5414	$255.54	$255.55	$255.50
Purchase #3	$98.44	6.266%	$104.6083	$104.61	$104.60	$104.60
Purchase #4	$48.50	3.115%	$50.0108	$50.01	$50.00	$50.00
Purchase #5	$47.34	10.358%	$52.2435	$52.24	$52.25	$52.20
Purchase #6	$113.37	12.788%	$127.8678	$127.87	$127.85	$127.90
Purchase #7	$216.46	10.436%	$239.0498	$239.05	$239.05	$239.00
7 purchase totals =	$880.06		$969.2096	$969.21	$969.20	$969.10