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	$68.63	3.530%	$71.0526	$71.05	$71.05	$71.10
Purchase #2	$220.52	8.854%	$240.0448	$240.04	$240.05	$240.00
Purchase #3	$221.62	5.235%	$233.2218	$233.22	$233.20	$233.20
Purchase #4	$210.79	12.493%	$237.124	$237.12	$237.10	$237.10
Purchase #5	$94.88	11.203%	$105.5094	$105.51	$105.50	$105.50
Purchase #6	$224.54	11.683%	$250.773	$250.77	$250.75	$250.80
Purchase #7	$100.67	10.300%	$111.039	$111.04	$111.05	$111.00
7 purchase totals =	$1,141.65		$1,248.7646	$1,248.75	$1,248.70	$1,248.70