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	$77.78	6.391%	$82.7509	$82.75	$82.75	$82.80
Purchase #2	$117.99	5.219%	$124.1479	$124.15	$124.15	$124.10
Purchase #3	$115.86	13.194%	$131.1466	$131.15	$131.15	$131.10
Purchase #4	$146.82	5.236%	$154.5075	$154.51	$154.50	$154.50
Purchase #5	$123.59	7.660%	$133.057	$133.06	$133.05	$133.10
Purchase #6	$156.44	10.301%	$172.5549	$172.55	$172.55	$172.60
Purchase #7	$72.85	10.260%	$80.3244	$80.32	$80.30	$80.30
7 purchase totals =	$811.33		$878.4892	$878.49	$878.45	$878.50