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	$138.53	4.469%	$144.7209	$144.72	$144.70	$144.70
Purchase #2	$220.59	4.693%	$230.9423	$230.94	$230.95	$230.90
Purchase #3	$100.93	8.316%	$109.3233	$109.32	$109.30	$109.30
Purchase #4	$227.89	4.585%	$238.3388	$238.34	$238.35	$238.30
Purchase #5	$69.78	10.187%	$76.8885	$76.89	$76.90	$76.90
Purchase #6	$77.83	10.442%	$85.957	$85.96	$85.95	$86.00
Purchase #7	$96.30	7.233%	$103.2654	$103.27	$103.25	$103.30
7 purchase totals =	$931.85		$989.4362	$989.44	$989.40	$989.40