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	$113.99	8.854%	$124.0827	$124.08	$124.10	$124.10
Purchase #2	$135.84	7.191%	$145.6083	$145.61	$145.60	$145.60
Purchase #3	$121.30	5.471%	$127.9363	$127.94	$127.95	$127.90
Purchase #4	$43.69	3.300%	$45.1318	$45.13	$45.15	$45.10
Purchase #5	$51.32	6.547%	$54.6799	$54.68	$54.70	$54.70
Purchase #6	$236.75	11.459%	$263.8792	$263.88	$263.90	$263.90
Purchase #7	$36.45	13.865%	$41.5038	$41.50	$41.50	$41.50
7 purchase totals =	$739.34		$802.8220	$802.82	$802.90	$802.80