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	$80.29	13.679%	$91.2729	$91.27	$91.25	$91.30
Purchase #2	$16.60	4.593%	$17.3624	$17.36	$17.35	$17.40
Purchase #3	$100.98	8.612%	$109.6764	$109.68	$109.70	$109.70
Purchase #4	$134.90	11.280%	$150.1167	$150.12	$150.10	$150.10
Purchase #5	$13.64	6.414%	$14.5149	$14.51	$14.50	$14.50
Purchase #6	$27.74	4.474%	$28.9811	$28.98	$29.00	$29.00
Purchase #7	$127.35	7.470%	$136.863	$136.86	$136.85	$136.90
7 purchase totals =	$501.50		$548.7874	$548.78	$548.75	$548.90