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	$156.76	13.291%	$177.595	$177.60	$177.60	$177.60
Purchase #2	$20.57	11.223%	$22.8786	$22.88	$22.90	$22.90
Purchase #3	$159.33	4.750%	$166.8982	$166.90	$166.90	$166.90
Purchase #4	$44.31	10.454%	$48.9422	$48.94	$48.95	$48.90
Purchase #5	$127.25	8.230%	$137.7227	$137.72	$137.70	$137.70
Purchase #6	$194.91	10.364%	$215.1105	$215.11	$215.10	$215.10
Purchase #7	$202.70	3.266%	$209.3202	$209.32	$209.30	$209.30
7 purchase totals =	$905.83		$978.4674	$978.47	$978.45	$978.40