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	$125.81	5.595%	$132.8491	$132.85	$132.85	$132.80
Purchase #2	$168.70	10.479%	$186.3781	$186.38	$186.40	$186.40
Purchase #3	$236.63	12.221%	$265.5486	$265.55	$265.55	$265.50
Purchase #4	$32.60	9.235%	$35.6106	$35.61	$35.60	$35.60
Purchase #5	$172.78	10.125%	$190.274	$190.27	$190.25	$190.30
Purchase #6	$79.60	13.257%	$90.1526	$90.15	$90.15	$90.20
Purchase #7	$91.38	11.699%	$102.0705	$102.07	$102.05	$102.10
7 purchase totals =	$907.50		$1,002.8835	$1,002.88	$1,002.85	$1,002.90