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	$238.38	6.769%	$254.5159	$254.52	$254.50	$254.50
Purchase #2	$166.88	5.671%	$176.3438	$176.34	$176.35	$176.30
Purchase #3	$69.67	9.624%	$76.375	$76.38	$76.40	$76.40
Purchase #4	$115.91	13.832%	$131.9427	$131.94	$131.95	$131.90
Purchase #5	$222.45	13.853%	$253.266	$253.27	$253.25	$253.30
Purchase #6	$38.89	11.668%	$43.4277	$43.43	$43.45	$43.40
Purchase #7	$17.83	3.107%	$18.384	$18.38	$18.40	$18.40
7 purchase totals =	$870.01		$954.2551	$954.26	$954.30	$954.20