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	$163.91	11.669%	$183.0367	$183.04	$183.05	$183.00
Purchase #2	$150.63	10.742%	$166.8107	$166.81	$166.80	$166.80
Purchase #3	$84.82	7.815%	$91.4487	$91.45	$91.45	$91.40
Purchase #4	$151.97	12.874%	$171.5346	$171.53	$171.55	$171.50
Purchase #5	$188.98	10.138%	$208.1388	$208.14	$208.15	$208.10
Purchase #6	$141.39	3.643%	$146.5408	$146.54	$146.55	$146.50
Purchase #7	$90.39	8.456%	$98.0334	$98.03	$98.05	$98.00
7 purchase totals =	$972.09		$1,065.5437	$1,065.54	$1,065.60	$1,065.30