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	$242.45	5.231%	$255.1326	$255.13	$255.15	$255.10
Purchase #2	$155.63	9.717%	$170.7526	$170.75	$170.75	$170.80
Purchase #3	$247.96	3.619%	$256.9337	$256.93	$256.95	$256.90
Purchase #4	$94.76	5.802%	$100.258	$100.26	$100.25	$100.30
Purchase #5	$128.48	13.154%	$145.3803	$145.38	$145.40	$145.40
Purchase #6	$177.34	11.752%	$198.181	$198.18	$198.20	$198.20
Purchase #7	$36.38	5.722%	$38.4617	$38.46	$38.45	$38.50
7 purchase totals =	$1,083.00		$1,165.0999	$1,165.09	$1,165.15	$1,165.20