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	$19.48	10.273%	$21.4812	$21.48	$21.50	$21.50
Purchase #2	$19.39	7.179%	$20.782	$20.78	$20.80	$20.80
Purchase #3	$225.50	11.684%	$251.8474	$251.85	$251.85	$251.80
Purchase #4	$62.29	5.190%	$65.5229	$65.52	$65.50	$65.50
Purchase #5	$119.50	3.272%	$123.41	$123.41	$123.40	$123.40
Purchase #6	$102.37	10.853%	$113.4802	$113.48	$113.50	$113.50
Purchase #7	$235.73	4.593%	$246.5571	$246.56	$246.55	$246.60
7 purchase totals =	$784.26		$843.0808	$843.08	$843.10	$843.10