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	$116.28	12.645%	$130.9836	$130.98	$131.00	$131.00
Purchase #2	$193.84	11.175%	$215.5016	$215.50	$215.50	$215.50
Purchase #3	$242.94	10.746%	$269.0463	$269.05	$269.05	$269.00
Purchase #4	$50.50	8.403%	$54.7435	$54.74	$54.75	$54.70
Purchase #5	$70.78	9.787%	$77.7072	$77.71	$77.70	$77.70
Purchase #6	$151.47	10.184%	$166.8957	$166.90	$166.90	$166.90
Purchase #7	$64.71	12.476%	$72.7832	$72.78	$72.80	$72.80
7 purchase totals =	$890.52		$987.6611	$987.66	$987.70	$987.60