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	$66.55	4.424%	$69.4942	$69.49	$69.50	$69.50
Purchase #2	$165.87	12.304%	$186.2786	$186.28	$186.30	$186.30
Purchase #3	$33.96	7.823%	$36.6167	$36.62	$36.60	$36.60
Purchase #4	$40.55	4.570%	$42.4031	$42.40	$42.40	$42.40
Purchase #5	$76.48	5.722%	$80.8562	$80.86	$80.85	$80.90
Purchase #6	$98.96	12.591%	$111.4201	$111.42	$111.40	$111.40
Purchase #7	$90.97	12.589%	$102.4222	$102.42	$102.40	$102.40
7 purchase totals =	$573.34		$629.4911	$629.49	$629.45	$629.50