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	$136.40	11.841%	$152.5511	$152.55	$152.55	$152.60
Purchase #2	$100.79	8.272%	$109.1273	$109.13	$109.15	$109.10
Purchase #3	$132.45	7.327%	$142.1546	$142.15	$142.15	$142.20
Purchase #4	$108.26	4.284%	$112.8979	$112.90	$112.90	$112.90
Purchase #5	$15.59	12.452%	$17.5313	$17.53	$17.55	$17.50
Purchase #6	$79.55	3.531%	$82.3589	$82.36	$82.35	$82.40
Purchase #7	$213.66	6.656%	$227.8812	$227.88	$227.90	$227.90
7 purchase totals =	$786.70		$844.5023	$844.50	$844.55	$844.60