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	$83.98	6.716%	$89.6201	$89.62	$89.60	$89.60
Purchase #2	$31.80	9.273%	$34.7488	$34.75	$34.75	$34.70
Purchase #3	$183.27	9.109%	$199.9641	$199.96	$199.95	$200.00
Purchase #4	$119.27	7.668%	$128.4156	$128.42	$128.40	$128.40
Purchase #5	$25.83	4.729%	$27.0515	$27.05	$27.05	$27.10
Purchase #6	$196.79	5.833%	$208.2688	$208.27	$208.25	$208.30
Purchase #7	$228.43	9.649%	$250.4712	$250.47	$250.45	$250.50
7 purchase totals =	$869.37		$938.5401	$938.54	$938.45	$938.60