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	$222.95	8.289%	$241.4303	$241.43	$241.45	$241.40
Purchase #2	$112.29	12.620%	$126.461	$126.46	$126.45	$126.50
Purchase #3	$119.86	9.729%	$131.5212	$131.52	$131.50	$131.50
Purchase #4	$87.26	12.862%	$98.4834	$98.48	$98.50	$98.50
Purchase #5	$53.81	9.395%	$58.8654	$58.87	$58.85	$58.90
Purchase #6	$151.41	11.289%	$168.5027	$168.50	$168.50	$168.50
Purchase #7	$174.72	12.511%	$196.5792	$196.58	$196.60	$196.60
7 purchase totals =	$922.30		$1,021.8432	$1,021.84	$1,021.85	$1,021.90