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	$95.69	6.713%	$102.1137	$102.11	$102.10	$102.10
Purchase #2	$82.79	11.750%	$92.5178	$92.52	$92.50	$92.50
Purchase #3	$14.73	7.787%	$15.877	$15.88	$15.90	$15.90
Purchase #4	$152.69	7.697%	$164.4425	$164.44	$164.45	$164.40
Purchase #5	$44.65	13.282%	$50.5804	$50.58	$50.60	$50.60
Purchase #6	$87.49	3.475%	$90.5303	$90.53	$90.55	$90.50
Purchase #7	$136.55	4.744%	$143.0279	$143.03	$143.05	$143.00
7 purchase totals =	$614.59		$659.0896	$659.09	$659.15	$659.00