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	$76.60	8.330%	$82.9808	$82.98	$83.00	$83.00
Purchase #2	$56.83	13.574%	$64.5441	$64.54	$64.55	$64.50
Purchase #3	$203.76	8.694%	$221.4749	$221.47	$221.45	$221.50
Purchase #4	$38.39	6.458%	$40.8692	$40.87	$40.85	$40.90
Purchase #5	$104.57	6.481%	$111.3472	$111.35	$111.35	$111.30
Purchase #6	$174.46	5.176%	$183.49	$183.49	$183.50	$183.50
Purchase #7	$249.58	5.837%	$264.148	$264.15	$264.15	$264.10
7 purchase totals =	$904.19		$968.8542	$968.85	$968.85	$968.80