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	$38.41	9.728%	$42.1465	$42.15	$42.15	$42.10
Purchase #2	$21.28	4.569%	$22.2523	$22.25	$22.25	$22.30
Purchase #3	$72.44	7.822%	$78.1063	$78.11	$78.10	$78.10
Purchase #4	$154.64	7.249%	$165.8499	$165.85	$165.85	$165.80
Purchase #5	$50.35	10.117%	$55.4439	$55.44	$55.45	$55.40
Purchase #6	$49.53	3.400%	$51.214	$51.21	$51.20	$51.20
Purchase #7	$211.98	6.679%	$226.1381	$226.14	$226.15	$226.10
7 purchase totals =	$598.63		$641.1510	$641.15	$641.15	$641.00