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	$51.79	5.726%	$54.7555	$54.76	$54.75	$54.80
Purchase #2	$75.65	12.836%	$85.3604	$85.36	$85.35	$85.40
Purchase #3	$43.85	10.470%	$48.4411	$48.44	$48.45	$48.40
Purchase #4	$58.68	3.708%	$60.8559	$60.86	$60.85	$60.90
Purchase #5	$171.67	12.119%	$192.4747	$192.47	$192.45	$192.50
Purchase #6	$215.31	4.754%	$225.5458	$225.55	$225.55	$225.50
Purchase #7	$136.32	4.207%	$142.055	$142.06	$142.05	$142.10
7 purchase totals =	$753.27		$809.4884	$809.50	$809.45	$809.60