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	$28.68	6.405%	$30.517	$30.52	$30.50	$30.50
Purchase #2	$88.65	10.770%	$98.1976	$98.20	$98.20	$98.20
Purchase #3	$231.91	9.166%	$253.1669	$253.17	$253.15	$253.20
Purchase #4	$27.84	3.699%	$28.8698	$28.87	$28.85	$28.90
Purchase #5	$31.60	12.590%	$35.5784	$35.58	$35.60	$35.60
Purchase #6	$178.71	9.684%	$196.0163	$196.02	$196.00	$196.00
Purchase #7	$81.27	11.362%	$90.5039	$90.50	$90.50	$90.50
7 purchase totals =	$668.66		$732.8499	$732.86	$732.80	$732.90