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	$140.68	4.151%	$146.5196	$146.52	$146.50	$146.50
Purchase #2	$72.41	12.401%	$81.3896	$81.39	$81.40	$81.40
Purchase #3	$79.62	8.629%	$86.4904	$86.49	$86.50	$86.50
Purchase #4	$241.27	12.274%	$270.8835	$270.88	$270.90	$270.90
Purchase #5	$213.41	11.653%	$238.2787	$238.28	$238.30	$238.30
Purchase #6	$179.47	9.436%	$196.4048	$196.40	$196.40	$196.40
Purchase #7	$112.37	8.342%	$121.7439	$121.74	$121.75	$121.70
7 purchase totals =	$1,039.23		$1,141.7105	$1,141.70	$1,141.75	$1,141.70