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	$250.72	8.846%	$272.8987	$272.90	$272.90	$272.90
Purchase #2	$103.81	8.457%	$112.5892	$112.59	$112.60	$112.60
Purchase #3	$250.88	9.275%	$274.1491	$274.15	$274.15	$274.10
Purchase #4	$234.78	13.654%	$266.8369	$266.84	$266.85	$266.80
Purchase #5	$219.50	12.136%	$246.1385	$246.14	$246.15	$246.10
Purchase #6	$148.77	3.598%	$154.1227	$154.12	$154.10	$154.10
Purchase #7	$173.40	13.151%	$196.2038	$196.20	$196.20	$196.20
7 purchase totals =	$1,381.86		$1,522.9389	$1,522.94	$1,522.95	$1,522.80