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	$137.34	5.471%	$144.8539	$144.85	$144.85	$144.90
Purchase #2	$31.87	7.791%	$34.353	$34.35	$34.35	$34.40
Purchase #3	$59.90	12.873%	$67.6109	$67.61	$67.60	$67.60
Purchase #4	$25.77	10.156%	$28.3872	$28.39	$28.40	$28.40
Purchase #5	$231.47	10.198%	$255.0753	$255.08	$255.10	$255.10
Purchase #6	$195.25	8.868%	$212.5648	$212.56	$212.55	$212.60
Purchase #7	$22.32	8.705%	$24.263	$24.26	$24.25	$24.30
7 purchase totals =	$703.92		$767.1081	$767.10	$767.10	$767.30