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	$46.53	10.751%	$51.5324	$51.53	$51.55	$51.50
Purchase #2	$38.39	4.704%	$40.1959	$40.20	$40.20	$40.20
Purchase #3	$196.68	11.523%	$219.3434	$219.34	$219.35	$219.30
Purchase #4	$57.41	9.746%	$63.0052	$63.01	$63.00	$63.00
Purchase #5	$224.78	11.627%	$250.9152	$250.92	$250.90	$250.90
Purchase #6	$91.89	12.822%	$103.6721	$103.67	$103.65	$103.70
Purchase #7	$104.54	12.494%	$117.6012	$117.60	$117.60	$117.60
7 purchase totals =	$760.22		$846.2654	$846.27	$846.25	$846.20