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	$124.60	5.138%	$131.0019	$131.00	$131.00	$131.00
Purchase #2	$90.98	11.611%	$101.5437	$101.54	$101.55	$101.50
Purchase #3	$96.33	4.522%	$100.686	$100.69	$100.70	$100.70
Purchase #4	$118.51	6.730%	$126.4857	$126.49	$126.50	$126.50
Purchase #5	$57.29	8.600%	$62.2169	$62.22	$62.20	$62.20
Purchase #6	$234.71	12.621%	$264.3327	$264.33	$264.35	$264.30
Purchase #7	$232.99	9.537%	$255.2103	$255.21	$255.20	$255.20
7 purchase totals =	$955.41		$1,041.4772	$1,041.48	$1,041.50	$1,041.40