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	$156.56	5.168%	$164.651	$164.65	$164.65	$164.70
Purchase #2	$101.60	7.854%	$109.5797	$109.58	$109.60	$109.60
Purchase #3	$48.27	13.563%	$54.8169	$54.82	$54.80	$54.80
Purchase #4	$95.80	7.185%	$102.6832	$102.68	$102.70	$102.70
Purchase #5	$30.59	3.712%	$31.7255	$31.73	$31.75	$31.70
Purchase #6	$38.74	3.191%	$39.9762	$39.98	$40.00	$40.00
Purchase #7	$136.71	7.722%	$147.2667	$147.27	$147.25	$147.30
7 purchase totals =	$608.27		$650.6992	$650.71	$650.75	$650.80