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	$7.60	12.173%	$8.5251	$8.53	$8.55	$8.50
Purchase #2	$237.77	7.303%	$255.1343	$255.13	$255.15	$255.10
Purchase #3	$222.25	10.758%	$246.1597	$246.16	$246.15	$246.20
Purchase #4	$142.76	4.330%	$148.9415	$148.94	$148.95	$148.90
Purchase #5	$175.70	5.654%	$185.6341	$185.63	$185.65	$185.60
Purchase #6	$109.67	3.682%	$113.708	$113.71	$113.70	$113.70
Purchase #7	$70.79	11.447%	$78.8933	$78.89	$78.90	$78.90
7 purchase totals =	$966.54		$1,036.9960	$1,036.99	$1,037.05	$1,036.90