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	$44.56	11.741%	$49.7918	$49.79	$49.80	$49.80
Purchase #2	$180.87	8.649%	$196.5134	$196.51	$196.50	$196.50
Purchase #3	$228.76	10.800%	$253.4661	$253.47	$253.45	$253.50
Purchase #4	$176.50	8.376%	$191.2836	$191.28	$191.30	$191.30
Purchase #5	$179.98	5.305%	$189.5279	$189.53	$189.55	$189.50
Purchase #6	$19.95	7.860%	$21.5181	$21.52	$21.50	$21.50
Purchase #7	$101.92	12.358%	$114.5153	$114.52	$114.50	$114.50
7 purchase totals =	$932.54		$1,016.6162	$1,016.62	$1,016.60	$1,016.60