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	$105.90	5.347%	$111.5625	$111.56	$111.55	$111.60
Purchase #2	$215.57	7.268%	$231.2376	$231.24	$231.25	$231.20
Purchase #3	$90.37	12.689%	$101.837	$101.84	$101.85	$101.80
Purchase #4	$112.60	11.817%	$125.9059	$125.91	$125.90	$125.90
Purchase #5	$70.92	11.248%	$78.8971	$78.90	$78.90	$78.90
Purchase #6	$19.81	4.604%	$20.7221	$20.72	$20.70	$20.70
Purchase #7	$30.28	3.422%	$31.3162	$31.32	$31.30	$31.30
7 purchase totals =	$645.45		$701.4784	$701.49	$701.45	$701.40